Twardowski's Paper

1. Introduction

   In colloquial speech and scholarly work alike, one finds the view that we can comprehend, form concepts of, some things which we cannot imagine. For example, we are unable to imagine God and infinity, atoms and the human soul, the ether and virtue, a quantity called "one thousand", a mathematical point and many other objects (1). We have, however, more or less precise concepts of God, of infinity, etc.; we use those concepts in reasoning and thereby compensate for the lack of certain imageries.
   This conviction ­ that we cannot imagine everything, and that concepts compensate where imagery is inaccessible to us ­ is nothing new. Contemporary psychology can claim no credit for this discovery. Aristotle was the first clearly to oppose imageries (phantasmata) to that which can only be understood (ta noeta) (2). The philosophy of the late Middle Ages follows his teaching in this respect. At the beginnings of modern philosophy, Descartes does not fail to stress the difference between imagining (imaginatio) and pure comprehending or understanding (pura intellectio). He expresses this as follows:

When I imagine a triangle, I do not just understand that it is a figure enclosed in three lines; I also at the same time see the three lines present before my mind's eye, and this is what I call imagining them. Now if I want to think of a chiliagon, I understand just as well that it is a figure of a thousand sides as I do that a triangle is a figure of three sides; but I do not in the same way imagine the thousand sides, or see them as presented to me. I am indeed accustomed al-ways to imagine something when I am thinking of a corporeal object; so it may confusedly picture to myself some kind of figure; but obviously this picture is not a chiliagon, since it is in no way different from the one I should form if I were thinking of a myriagon, or any other figure with many sides; and it in no way helps me to recognize the properties that distinguish a chiliagon from other polygons. If now it is a pentagon that is in question, I can understand its figure, as I can the figure of a chiliagon, without the aid of imagination; but I may also imagine this very figure, applying my mind's eye to its five sides and at the same time to the area contained by them; and here I clearly discern that I have to make some special effort of mind to imagine it, that I do not make in just understanding it; this new mental effort plainly shows the difference between imagination and pure understanding. (3)

   The words Taine dedicates to this matter are all but a mere repetition of Descartes' considerations:

A myriagon is a polygon with ten thousand sides. It is impossible to imagine this, even if we would like to, as an individual myriagon of a certain colour; even less are we able to imagine it abstractly, in general. Even were the inner eye unimaginably clear and exact, after five or six, twenty or thirty lines drawn with great effort, the picture grows muddled and fades. Yet my concept of a myriagon has nothing muddled or faded; my concept does not hold the myriagon I imagine, unfinished and disintegrating, but a finished myriagon whose parts exist together; I imagine the first very poorly and I understand the second very well. What I understand is something different from this what I imagine; my concept is not at all this unresolved figure which accompanies it. (4)

   The very fact is beyond all question: there are objects which we cannot imagine, which are accessible to our minds through the mediation of concepts. This is a commonly recognized truth. Among the views of psychologists, agreement prevails on this matter. This yields to a difference of opinions when, dissatisfied with the mere ascertainment of the fact, we ask: What are these concepts, by which our mind transcends the limits of the imaginable, into the sphere of what can only be comprehended?
   In this regard, such a diversity of views exists that at first the view of Mill, who saw the very existence of the term 'concept' as a great misfortune, might seem attractive (5). Yet after closer examination of numerous theories of the nature of concepts, we discover an explanation for their differences; scholars occupied with the matter either consider only concepts of certain kinds, or of a limited de-gree of development. Thus, some scholars, such as Ribot, analyze general con-cepts; others, including Sigwart and Rickert, consider scientific concepts, the re-sults of scholarly research; others again, such as Taine, limit debate on concepts to those characterized by the domination of a word over the content attached thereto, and so forth (6). Thus, we cannot be surprised that such scholars arrive at different conclusions; despite a common point of departure, the nature of con-cepts, the paths they follow diverge more or less, according to the kinds of con-cepts which each has in mind.
   Thus, the differences obtaining among these thinkers' approaches to the nature of concepts need not be irreconcilable under all conditions. We should not exclude that each of these competing theories of concepts is correct, but with respect only to concepts of a certain kind, or a certain degree of development. In this case, no existing theory would suffice to explain the nature of concepts in general. Nor can we exclude that these theories are so related that one entails all others as special cases; up to now, it has simply not been shown how these cases are entailed. Both cases would prove the abovementioned differences only apparent; individual theories on the nature of concepts, now coexisting or even opposing to each other, could fit into a more general theory from which they could be inferred. One need only found such a general theory, or choose among those already existing, and show how theories concerning particular kinds of con-cepts follow therefrom. The present considerations are meant to fulfil this goal.
   The aim then is to develop and justify a view of the nature of concepts, embracing and explaining within a uniform theory all conceptual comprehension of objects. Of course, all that has been conceived, wherever by whomever, cannot be listed or analyzed individually; however, no kind or type of concept should be omitted. For only an exhaustive review can assure that a proposed general theory of concepts comply with all requirements which should rightly be imposed. On the other hand, recognizing how a general theory applies to different kinds of concepts will enable us to treat of any concept without difficulty.
   Our starting point is that concepts enable us to think about objects we are unable to imagine. Thus, to outline precisely the field of inquiry, we should first gauge the limits of our power of imagining. All that lies beyond is accessible only to concepts. On the other hand, we are eager to avoid the misunderstandings which can arise from the lack of a fixed terminology. We begin with some explanation of the meaning of the words "imagery" and "concept" (7).

2. On some definitions of imageries

   To investigate the psychological processes enabling us to think and talk about objects that we cannot imagine, and to list the primary types of concepts, we must first concern ourselves with imagery. We are forced to do so by the relation which imageries bear to concepts. This relation may be more closely delimited after concepts themselves are investigated. Yet even now we should not overlook the fact that all psychologists have always taken imageries to be a basis and a necessary condition for concepts. Aristotle's oudepote noei aneu phantasmatos he psyche is still valid; psychological research has progressed to yield more and more new arguments for the truth of this claim. Thus, if imagery is an indispensable basis for all thinking using concepts, however abstract, then the analysis of concepts cannot disregard imagery.
   To account for the nature of imagery, as the aim of this paper requires, we will briefly survey the most common definitions of imagery. One often finds the claim that imageries are reproduced impressions, recollections of impressions. Such a definition of imagery resembles Hume's distinction between impressions as primary mental phenomena and imageries (ideas) as their restoration. For Hume, the term impression refers to primary data of both external and internal experience. He distinguishes impressions of sensations from impressions of reflexion; among the former he counts impressions of colour, sound, and so forth, among the latter impressions e.g. of pain, anger, sadness and joy (8). Contemporary thinkers who refer to restored or renewed impression, generally mean by impressions only sensations, sensory perceptions (9).
   All definitions which describe imagery as restored, renewed, or recollected impressions are in error, for they are based on a totally mistaken understanding of the relation between imagery and impression.
   The exponents of this definition describe the relation as follows. Seeing certain colours, hearing certain sounds, etc. we experience sensory impressions caused by external stimuli and changes in the nervous system. Having once experienced such impressions, we remember them and can realize them again, without the aid of any external stimuli. Realizing previous impressions by memory does not involve the external stimuli whose action is a condition of impression. We create in the mind a copy, as it were, of previously experienced impressions; it is, so to speak, an image of past impressions which allows us to realize them; these copies are imageries. Thus, we speak of colour or sound impressions when they reach our consciousness through the effect of stimuli. On the other hand, we speak of colour or sound imageries realized without any stimuli.
   Yet such an understanding of imageries and their relation to impressions disregards the fact that we speak of imagery, not only of colours, sounds, tastes, smells, etc. but also of tables, books, melodies, landscapes etc. I do not deny that renewed impressions play a key role in imagery of this kind; I freely admit that such imagery could not exist without restored impressions. Yet I do not find that the essence of imagery consists in the restoration of impressions; quite often, we imagine certain objects without restoring the impressions which we experienced in perceiving them.
   For example, the memory of sounds may be absolute or relative; persons with perfect pitch exemplify the former. Hearing any sound, such a person can indicate its pitch. Someone without perfect pitch would not recognize the pitch of a sound he hears, because he cannot remember it. On the other hand, even without perfect pitch, relative memory enables him to store relations between sounds with respect to their pitch. Thus, he can remember and differentiate intervals, melody, harmony. When we ask a person with perfect pitch to sing from memory a song which he once heard, he will render not only the exact melody, but also the exact key in which he heard the song. A person with relative memory for sound will sing the same song, but may do so in a key lower or higher by a fourth or a fifth.
   Someone who recalls a melody he has heard, whether in the same key or in a different one, obviously possesses some image of this melody. In imagining it a few tones higher or lower, he does not restore in the memory the impressions he experienced while hearing the melody. Perhaps he heard the melody played or sung in C-major, but imagines it in his memory in G-major; in this case, then, an image of the melody exists, though the impressions experienced in the moment of perceiving (hearing) the melody have not been restored. From this it clearly follows that imagery cannot be reduced to restored impression, if it can exist in cases where the relevant impressions are not restored.
   Thus, those who wish to avoid this difficulty define imagery as renewal, restoration or recollection of perceptions. For example, Schmitz-Dumont says: "By 'imagery' I mean a sensory reproduction of perception. Yet it is not difficult to prove that this definition of imagery, as much as the last, rests on but a superficial analysis of the relation of imagery to perception" (10).
   The act of perception is quite complex; it was only contemporary psychology that reached the conclusion that judgements take part in perception. Some plain-spoken thinkers, such as Taine and Höfler (11), say this explicitly, others do not speak of judgements when analyzing perceptions, yet still list elements of perception which, no doubt, are judgements. For example, Sully expresses himself as follows: "To perceive an orange means to refer a group of impressions of light, shade and colour to the object called an orange, located in a concrete part of space"; thus, he sees the essential elements of perception in locating impressions and referring them to an object.
   To refer impressions to a certain object or to a place is to maintain that what we see is this object or that, located in this place or that. That we deal with a judgement here is seldom explicitly stated; it is confirmed by the fact that perception can be erroneous, as numerous sensory illusions testify. Error and truth alike are qualities characteristic of judgements; only judgements can be true or false in the proper sense of the term. It cannot then be doubted that perceptions entail judgements.
   Thus, if imagery were a restoration of perception, it should restore also judgements contained in that perception. But it is not so; it can be said outright that imagery differs from perceptions in its refraining from judgement. For example, one who perceives a cloud is at the same time convinced of its existence; were he not, he would not perceive, but hallucinate. One who imagines a cloud does not at all need to be convinced of its existence; he may even know that the cloud which he imagines does not exist at all. The same applies to judgements which locate objects perceived. For example, one who perceives a person sitting opposite him at a table, believes, that is, makes a judgement (13), that this person is in a given moment exactly at this place. One who only imagines a person sitting opposite him at the table, does not make such a judgement, knowing well that the person he imagines may be, for example, somewhere else, or even dead.
   Thus, the absence of judgements which would refer to an imagined object is among the principal features distinguishing imagery from perception. This is why imagery cannot be a simple renewal, restoration, or recollection of a perception made in the past.
   What, then, is imagery? To pave the way to a correct answer to this question, it would be best to start by considering again the constitutive elements of perception.

3. Imagery as a synthesis of impressions

   Both definitions of imagery described in the previous section have proven erroneous. Imagery is neither restored impression nor restored perception; it is not the former, since we often imagine objects (such as melodies) without renewing in the memory the impressions by which these objects were originally given to us; it is not the latter, as in the restraint of judgement imagery so differs from perception that we cannot consider it a reconstruction of perception. In fact, both definitions are less the results of precise psychological analysis, than tailored to certain requirements of a theory of cognition which supposes that all imagery directly or indirectly has its source in perception. Since modern psychology has been developed on the basis of such a theory of cognition (14), it is not surprising that we find here just such definitions of imagery.
   Yet the requirements of our theory of cognition should be consistent with the results of psychological research; thus, here, too, there must be a way to reconcile the two, or else our theory of cognition would have to give way to the results of psychological analysis. If the source of imagery is perception, and imagery reconstructs neither perceptions nor impressions contained in those perceptions, then our theory of cognition and our psychological data can agree only if some third element in perception can be found, apart from judgements and impressions, which allows us to root imageries in perceptions. And indeed, sensory impressions and specific judgements do not exhaust the entirety of perception.
   When we perceive an object, we are given a set of impressions; for instance, in perceiving an orange, we experience certain visual impressions. These do not exist apart from one another; they form a whole, but not a sum in a mathematical sense; as some English psychologists say, they undergo integration. This process usually happens so quickly that it escapes our attention. One who perceives an orange cannot distinguish the moment in which individual impressions are given to him, from that in which these impressions integrate into a whole. Nevertheless, we do not lack for cases in which the difference between both moments vividly occurs.
   For example, in discerning a figure hidden in a landscape, in the first moment we receive impressions originating from the lines and points which constitute that figure. Despite this, however, we cannot detect [the figure] itself; we do not see it, because we are unable to apprehend these lines and points as a whole, since they belong to some other wholes forming the individual parts (trees, rocks, etc.) of the landscape. Only once the mind has united the individual impressions created by the lines and points belonging to the figure into a whole, when it has integrated them, do we see the figure in the landscape.
   Another example is given in auditory impression. We sometimes say we cannot grasp a melody in a complicated musical work. When we listen to such a composition, we certainly receive the very auditory impressions which together form the melody; we hear them as much as one who can immediately grasp the melody. Despite this, we do not hear the melody. The sounds which correspond to our impressions do not form a whole; they follow each other with no connection, lacking any unity. We comprehend the melody only once the individual impressions of sounds are integrated, when they stop being a succession of separated, disconnected impressions, when our mind comprehends them on the whole and they become parts of [this whole].
   In these cases, individual impressions received simultaneously or in direct succession evidently coalesce into one whole; in other cases, this process is not so vivid. Yet it seems that a developed mind never receives impressions which undergo no integration whatsoever. One may show that, even in seeing a barely noticeable point, or hearing a simple sound, such integration is not absent (15).
   Thus, perception consists of three elements: impressions, synthesis ­ integration of impressions into a whole, and judgements. Thus, if imagery is neither restored perception in general nor simple restoration of impressions, then nothing remains but to treat it precisely as a synthesis of impressions (16). This is how Wundt, Scripture, Struve and many others understand the issue, defining imagery as the synthesis of sensory impressions. By accepting the above definition, we avoid the objection that we can imagine a melody without restoring any of the impressions experienced in the moment we heard this melody. As synthesis of impressions, imagery is indeed based on impressions, immediate or renewed, but it is no simple reconstruction; thus, it may be based on any impression for which the relevant whole can be reconstructed.
   As a synthesis of impressions, imagery still remains something distinct from impression. The difference between imagery and impression, however, is not that impression occurs under the influence of external stimuli and without such stimuli. It consists in the fact that describes wholes which are combined from elements, and impressions are just these elements. The relation of imagery to impressions is that of a whole to its parts.
   One could ask how impressions synthesize to create imagery; psychology has not yet and probably never will answer this question. The origin of imagery seems to belong to those mental phenomena which resist all analysis, all description. We know them well from our own experience, but we cannot analyze them or tell what they are. Description must be replaced by exemplification; when we call imagery a 'synthesis' of impressions, we can explain this synthesis only by means of examples. For example, when one sees a coloured surface, one receives a great number of visual impressions, since from any point of this surface, stimuli, beams of light, are reaching the retina. Despite this, not a mosaic of impressions but a consistent imagery, a coloured surface, appears in the mind; all the impressions are integrated into one whole. In the other senses, it is much the same. This synthesis is marked by the exact unification of the impressions which enter into its composition; in a sense, impressions conjoin with each other and this is why imageries are sometimes called 'concrete', that is, 'conjoined'.
   A definition attributing to imagery the synthesis of sensory impressions does not allow us to see imageries as traces of vanished impressions or perceptions remaining in the mind or the brain. Imagery already exists simultaneously with perception, as an original part thereof. One who perceives a pencil or a book already has an image of a pencil or a book from the moment he perceives one; this is just as true of any other perception. Imagery appearing in the mind in the moment of perception, as distinguished from other imageries, is called presentation (Wahrnehmung-Vorstellungen, sense-images).
   Imagery can also exist without an accompanying perception. We can restore impressions previously experienced; it is not yet clear what these recollected, restored, renewed impressions are. Some consider them but a weaker repetition of old impressions. According to this theory, immediate impressions experienced as a result of the influence of external stimuli differ only in degree from restorations. Others hold that immediate and restored impressions differ in their very essence. However this controversy may be resolved, there is no doubt that we can realize, that is restore or renew, impressions previously experienced. Yet since we never experience impressions in isolation, but only in certain contexts, in like manner we realize impressions only to some degree, in some integration which constitutes their synthesis.
   A synthesis of such recollected impressions can take two forms, either like unto or differing from the synthesis in which they were originally integrated, as effects of external stimuli. In the first case, the synthesis of restored impressions renews that of the primary original impressions, and is called "reproductive imagery" (Erinnerung-Vorstellung, memory image, representation, wyobraz-enie odtwórcze); in the other case, the synthesis appears as something new, as a spontaneous or intended product of fancy, and is called creative imagery.
   The definition which describes imagery as a synthesis of impressions does not contradict the established facts of psychology; it further unites in one natural class three groups of mental facts with common essential features (perceptual, reproductive and creative imagery). Thus, it should be given priority over other definitions of imagery. Yet we will soon discover that imagery so defined takes into account only one kind thereof, and omits another of no less importance.

4. Imageries of mental objects

   We have already mentioned the modern theory of cognition, which holds that all our imagery originates, directly or indirectly, from perceptions. Based on our considerations in the last section, we can formulate this rule as follows: all reproductive or creative imagery has its origin respectively in the simple realization, or in the changing and combining of perceptual imagery. We also mentioned the common, unanimous opinion among psychologists, that is the basis of all concepts. This does not mean in the least that each concept has a precisely determined imagery; rather, the claim is that, given any concept, we should be able to indicate the imagery from which it originated, perhaps through very complicated development ­ that is, if we do not wish to resort to the now universally and rightly rejected hypothesis of innate concepts.
   Thus, any concept must be traced back to imagery, and any imagery is either itself perceptual, or has originated from perceptual [imageries] by means of the memory alone, or the memory and the fancy together. This refers not only to conceptions of material objects, but also to those of mental objects. For there are also such concepts; we have more or less established concepts of impressions, concepts, judgements, conclusions, feelings, etc. The whole of psychology rests on this. Thus, such concepts, as all other concepts of mental objects, must be traceable to imagery; there must be some basis enabling us to think of things we call non-sensory or mental.
   The question arises: what imageries form the basis for our mind to create such concepts? From what are they derived? What gives them a concrete foundation? So far, we have spoken of imagery exclusively as a synthesis of sensory impressions; perhaps these form a basis for developing concepts of mental objects. Two things seem to speak for this.
   First, the fact is that most words denoting mental objects are derived from others referring to material objects ­ such objects as trace their imagery to syntheses of sensory impression. Good examples are words such as "imagination" (image), "concept" (take up), "being moved" (movement), "inclination", "hesitation", "decision", etc. As the names of mental objects are derived from those of material objects, so too could concepts of mental objects be derived from physical object imagery. The fact that each individual and mankind as a whole discovered physical object imagery much earlier than concepts of mental object might also supported this claim.
   Second, it is well known that we form concepts of objects with certain properties, based on imageries of objects with opposite properties. In this way, the imagery of finite beings serve as a basis for creating the concept of an infinite being. One could assume that concepts of non-sensory, mental, immaterial objects, were traceable to images of sensory, physical, material objects. The analogy seems adequate; if so, we can consider the imagery of physical objects the source of our concepts of mental objects.
   Yet it is not so; the argument just quoted would be valid only if our concepts of mental objects had a purely negative, oppositive content. If so, a concept of any mental object could originate from a simple negation of sensory features. Yet in our conception of mental objects we find a number of positive qualities, apart from the negative property of being non-sensory. Among these are, for example, the truth and falsity of a judgement, the intensity of an impression, etc. Thus, concepts of mental objects are not created by a simple negation of sensory features.
   The first argument also proves nothing; not all words referring to the mental world originate from words referring to phenomena of the sensory world. Yet if some mental objects (thought, emotion, etc) have names not drawn from those of physical objects, then the whole argument for a mutual genetic relation of concepts to names collapses. On the other hand, the fact that concepts of physical objects precede those of mental objects in mental development does not at all prove that the latter originate from the former; altruistic emotions develop later than egoistic emotions, yet no one sees this as a sufficient argument that altruistic emotions originate from egoistic emotions.
   If, therefore, concepts of mental objects cannot be derived from imageries of physical objects, then one must accept the existence of an imagery of mental objects, from which we derive concepts of such objects. It is not commonly accepted to speak of such imagery, such as an image of a certain emotion or of a certain judgement, because we are accustomed to the word "imagery" as attached to the idea that the imagined object is sensory. Yet it does not hurt to recall that in colloquial Polish the word "image" [in the sense of picture ­ translator] is generally associated almost exclusively with vision; despite this, one does not hesitate to associate imagery with objects not susceptible to sight (melody, taste, weight imagery); it has been discovered that certain psychic effects follow aural (etc.) impressions, with the same qualities as imageries derived from visual perception. The motives which allow us to use the word "imagery", not only in the sphere of sight but in all the other senses, induce us to reapply this term from sensory experience to inner experience. As some manifestations of mental life refer to non-sensory objects as imagery does to sensory objects, we must consider also those manifestations as imagery.
   So far, we have proven deductively the existence of imagery referring to mental objects as follows: Since there are concepts of mental objects, and all concepts are based on imagery, there must also be imagery for mental objects. This proof, however, needs some completion: we seek indications for imagery of mental objects, a posteriori confirmation of our deduction's correctness. We must point out manifestations of mental life which would be in all respects identical to imagery of sensory objects, but refer to non-sensory objects.
   The most vivid example of imagery of mental objects belongs to manifestations of mental life, by which we realize judgements previously made, emotions once experienced, decisions made in the past. Such events occur often; their existence is not in question. One who considers Krakus a figure of imagination can recall once having believed in his existence, and can realize the judgements about Krakus (17) which he made at that time. Similarly, we can recall in memory emotions which shook us at important moments in our life, such as a friend's death. Our decisions appear in memory, whenever we experience qualms of conscience or satisfaction from resolutions once made. A little self-reflection shows the common phenomenon of spontaneous or intended recollection of past events in mental life.
   Comparing such cases to others in which we realize in memory physical phenomena once perceived, we find a perfect analogy. Our mental activities must be perceived more or less clearly in the moment of their occurrence, in order to be stored and reconstructed in memory. In each case, there is perception of an object; in each case, something presentifies the object to the mind in the absence of object and perception alike. For sensory objects, (reproductive) imagery 'makes the object present'; why should such imagery not perform the same function for mental objects?
   Mental objects express not only reproductive, but also perceptual and creative imagery. The perceptual follows from the existence of the reproductive; for example, when we are aware of the anger which agitates us, when we realize we are angry, we have a perceptual imagery of the anger which, if renewed in the memory once the anger has disappeared, becomes reproductive.
   As an example of creative imagery of mental objects imagine the joy which you would experience in the moment when your fondest dreams came true. Knowing the emotion of joy from experience (from perceptual imagery), we realize this imagery in the memory, then apply them to new objects, transforming them in the phantasy.
   We must admit that imageries of mental objects are usually less distinct than those of physical objects; this fact surely contributes to a disinclination to accept imagery of mental objects. As it happens, inner perceptions are less adequate than sensory perceptions; this manifests itself e.g. in the impossibility of inner observation (18). With practice, however, one may develop a skill for very adequate inner perceptions and clear images of one's mental phenomena. Subtle analyses and detailed descriptions of mental life by brilliant psychologists and poets testify to this. The creative imagery through which Shakespeare depicted Hamlet's mental life is no less vivid or manifest than that which presented the figures of his Madonnas to Raphael.
   In accepting an imagery of mental objects alongside that of physical objects we follow Hume, for whom impressions and ideas refer to physical and mental objects alike. Thus, we cannot unconditionally define imagery as a synthesis of sensory impressions. Only imagery referring to physical objects is a synthesis of sensory impressions; besides this, however, there is another imagery, of mental objects.
   When I talk about images of pain, judgement, decision ­ in short, of mental objects ­ I know I leave myself open to sharp opposition on the part of those, like Raciborski, who claim that mental properties as such cannot be imagined (19). Yet Taine himself, who ex definitione restricts imagery to physical objects, comes in the course of his considerations also to speak of imagery of mental phenomena, and without hesitation uses such expressions as: "A group of images analogous to those by which we represent inner events to ourselves or the sensations and images which represent for us all the properties of the body, evoke the imageries which represent all the properties of the soul" (21). Thus, to speak of imagery for mental objects is not so inconceivable.
   Yet as imagery exists for physical objects as well as for mental, we must indicate the features common to both kinds of imagery. The following sections take up this task.

5. The concreteness of imagery

   The first two definitions of imagery described in the previous sections (restored impression and restored perception) have proven inadequate to reality, based on too superficial an approach to imagery as mental states. On the other hand, the third definition as a synthesis of sensory impressions is too narrow, for it does not address mental object imagery which obviously does not come from sensory impressions.
   Yet we may show that mental imagery shares a quality primarily characteristic of physical object imagery: each is constituted of multiple, relatively simple elements, and each integrates these elements into a whole, in a way which is familiar to all of us from experience but cannot be fully described. This character belongs to mental and physical object imagery alike, each in a different form but unchanged in its essence.
    For physical objects, sensory impressions play the role of constitutive elements. Any physical object imagery is constituted by a certain number of sensory impressions. The same quality belongs to mental imagery ­ here traced first of all to imagery of individual states of our mind. What consciousness discloses to us in a given moment as a content of our mind is a complex of elements, be it more or fewer.
   In any given moment, mental life, at least in those capable of inner perception, consists in mental activities of several kinds. For example, one who makes a judgement necessarily presents to himself an object of judgement; he cherishes imagery or concepts about an object, whatever his judgement may be. In the same way, only such a basis of imagery or concepts makes our decisions possible. Thus, if someone imagines a mental state in which he passes judgement, feels an emotion, or comes to a decision, the object of his imagery is complex; certain elements in the imagery ­ or, more precisely, in its content (21) ­ correspond to specific elements in an imagined object, just as impressions, caused by light waves sent from different points to the eye conform imagery to the elements of a sensory object, such as to the individual parts of a coloured surface. As physical object imagery consists of impressions, so an imagery of such mental states consists of certain elements corresponding to the elements of those states. This reasoning could be disputed; its result is not confirmed by inner experience, in that one cannot directly discern elements in imagery of any mental state.
    While one cannot but allow some validity to this remark, it does not refute our thesis of the complexity of mental imagery. For also some physical object imagery has long 'resisted' analysis, coming to be considered as simple impression. It suffices to mention sounds which consist of many tones: Most people, when they hear such a sound, do not think they receive a number of impressions; despite this, there is no doubt that the perceptual imagery for that sound is a complex of impressions corresponding to the individual tones. As we can seldom distinguish constitutive elements in physical object imagery, can we be surprised to encounter insurmountable difficulties analyzing mental objects? In the first case, analysis of the imagined object is aided by observation, whereby we recreate successively and thereby discern the elements of impression, originally simultaneous and thus indistinguishable. In contrast, the main, if not exclusive, referents of mental object imagery, mental states, are not open to observation.
   If so, the question could arise: how do we know mental object imagery is complex? How do we know that our deduction to that effect is valid and in accord with the real state of affairs? The answer is simple: When we compare various mental states, we discover many similarities. For example, when we compare the belief expressed in the proposition "A circle is a regular figure" to that expressed as "A square is a regular figure", we find the concept of a "regular figure" in both mental states. To compare these two mental states, we must imagine them; insofar as we imagine them similarly, these imageries must have something in common. Yet since these states are not identical, but only similar, something in their imageries must differ, despite everything they have in common. These imageries must entail multiple elements, at least one common, at least one different. Thus, we can ascertain in the imagery of mental states a multiplicity of elements we cannot directly discern.
   Examples for the analysis above were drawn from mental states, consisting in imagery or concepts in connection with a judgement, an emotion or a decision. For neither judgements, nor emotions, nor decisions can exist without an imagery or concept. Imagery can, however ­ at least in abstracto ­ exist without judgements, etc. Yet if we imagine a mental state which consists of only one image: is the imagery for such a state also complex?
    We cannot deny this, if we consider that any mental phenomenon occurs in time, and proceeds for a certain time, however short. We imagine it as consisting of parts following each other in time; therefore, our imagery must contain elements corresponding then to one part, then to another. Such imagery is then an integration of some number of elements.
   Thus, one can say that all imagery, of mental and physical objects alike, is an integration, synthesis, complex of numerous elements, in which the objects imagined are given to us in their parts. For physical objects, these elements are called impressions; for the corresponding elements in mental object imagery we have no name. In this integration of elements into a whole, we should see the characterizing feature of imagery, whose role in our mental life consists first of all in bringing order into the chaos of impressions and of the analogous elements which form the content of our mind. Only the apprehension of impressions and analogous elements in certain distinct, closed wholes makes it possible to distinguish one object from another (22).
   Perceptual imagery integrates these elements into wholes by the power of our psychophysical structure, not through conscious mental activity. Thus, in starting to investige our own imagery, we find completed wholes; only further psychological analysis indicates the elements which enter into their composition (23). As we have mentioned, the so-called concreteness of imagery consists in its compact integration of elements. Describing this concreteness negatively, we could say it consists in the indistinguishability of the elements entering into its composition. We thus call imagery concrete, insofar as analysis has yet to distinguish its elements. As the analysis of imagery into its constitutive parts is an abstraction, it may be said that imagery is concrete insofar as it has not been submitted to abstraction (25).

6. The manifestness (Anschaulichkeit) of imagery

   Another feature of imagery, besides the concreteness which expresses a particularly compact integration in its elements, is manifestness. For example, Meinong clearly distinguishes manifestness from concreteness, ascribing concreteness to imagery to the degree it has remained free from abstraction, and manifestness as far as it is free of inconsistency in its elements. Later, Meinong claims the manifestness of imagery is not necessarily connected to its concreteness, and thus there exists manifest imagery which is not concrete, but abstract (25).
   This distinction between manifestness and concreteness follows from a widespread concept of abstraction, accepted by Meinong, among others. This concept sees abstraction as bringing out certain features of an imagined object by concentrating attention on them, while neglecting other features. For example, an object X possesses the features a,b,c,d...; in imagining it, I may direct my attention to a and b, and away from c and d. In this case, a and b appear in my consciousness more clearly, more vividly, while c and d fade into the background, as it were.
   If one terms such unequal distribution of attention to individual features 'abstraction', one must surely allow for imagery which is at once manifest and non-concrete. For there is no doubt that when I see, for example, an apple lying before me, I have some manifest perceptual imagery of this object; if for any reason its shape is outlined more vividly in my consciousness than its colour, i.e. if some features of the object strike me more than others, then an abstraction has been performed on this imagery. In this case, then, the object would be manifest without concreteness.
   If we accept such an understanding, where abstraction is already given in an unequal distribution of attention, we would have to accept Meinong's reasoning. We will, however, see [in a further section which is omitted here ­ ed. note] that the process of abstraction requires something more; what Meinong and many others consider abstraction is no more than a necessary, but not at all sufficient, condition thereto. If we accepted Meinong's claim, we would be unable to avoid the consequence that all imagery is more or less abstract, that concrete imagery does not exist at all. Meinong himself admits that objects given to us in experience seldom attract our attention as a whole; what interests us is brought out without effort, while we ignore the rest (26). To me, it even seems safe to replace the word 'seldom' with 'never'; in that case, abstraction would be involved in any imagery. Ribot, who like Meinong reduces abstraction to a particular directing of our attention (une direction particuliére de l'attention), expresses this thought openly (27).
   As we do not accept such a concept of abstraction, we cannot apply it to any imagery. On the contrary, we must show how, under the influence of abstraction, changes into mental phenomena with the essential features of concepts. Thereby, we take any imagery as such as eo ipso concrete.
   Yet since we also ascribe manifestness ex definitione to all imagery, the thought arises that 'concreteness' and 'manifestness' may be synonymous. To support this, many writers have contrasted manifestness, as a feature of imagery, with abstraction. For example Schopenhauer divides the accessible modes of presenting objects in the mind into imagery and concepts, and calls the former manifest "in contrast to purely thought and therefore abstract concepts" (28). In realizing the meaning of the word 'manifest' and its relation to the word 'concrete,' we discover that in fact manifestness and concreteness are one and the same feature, whose double name rests on the two points of view from which it is considered. By the concreteness of imagery we mean a mutual relation among the elements constituting the imagery's structure, namely the close unity so often mentioned before. Abstraction loosens this close unity by distinguishing individual elements in the structure of imagery; thus, imagery is called concrete insofar as it appears as a undifferentiated whole. At once imagery is also manifest; the term 'manifestness' denotes the relation of any imagery, concrete as it is, to experience (perception) as the primary source of imagery.
   'Appearance,' which resembles the word 'apparent' (29) is pars pro toto; this word denotes first of all perceptual imagery stemming from visual impressions. Still, the term is used, if less often, with respect to perceptual imagery pertaining to the other senses (and also in a metaphorical sense ­ as a view or opinion is apparent to me). Thus, when we call imagery 'manifest' or 'apparent', we stress how each imagery is either directly perceptual, or recalls perceptual imagery to us, or at least behaves as if it were a recollection of perceptual imagery.
   Let us say we present something to ourselves, such as a giant, by means of creative imagery; the manifestness of this imagery consists in the fact that it could be reproductive or even perceptual if the object existed and was accessible to us. Creative does not differ from reproductive or perceptual imagery in its structure, but only in its origin in the mind. Imagery in the structure defines itself as concrete; such imagery, being concrete, is manifest ­ it either originated from perceptions, or could have done so under certain external conditions (if such an object existed and was accessible to our senses). Conversely, in being manifest imagery is at once concrete, since perception, in which we discern the manifestness of imagery, gives us exclusively concrete imagery.
   We ascribe concreteness to imagery, as opposed to the abstractness of concepts; we find imagery manifest, as opposed to the hiddenness of concepts. Concepts are hidden, so far as their proper objects are never given to us in perception. Otherwise we would imagine them ­ and not need concepts to present them to ourselves.

7. Sketchiness of imageries

   In the previous section, we mentioned that an object's individual features do not all attract our attention equally; thus they come to appear in its corresponding imagery with different degrees of vividness. When we perceive a given object, its imagery can generally be treated not as purely perceptual, but also partly reproductive. When I perceive, for example, an iron ball lying on the table in front of me, I imagine a number of features integrated into a concrete whole, but I do not simultaneously perceive all the features I imagine. I see the colour of the ball but I do not see its smoothness; its colour is given to me as perceptual imagery, and its smoothness as reproductive imagery; what brings it to my mind is seeing the object's colour, by which I know from previous perception (tactile) that the object is smooth. Both imageries, perceptual of colour, reproductive of smoothness, are integrated into one imagery; in this new imagery, they obviously do not prove equally vivid, if only that reproductive imagery ­ ceteris paribus ­ is less vivid than perceptual imagery.
   The qualities given to us exclusively in perceptual imagery vary also in the degree of vividness with which they appear to us, and this for two reasons: some impressions constitutive for the imagery are either more intensive, or are connected to stronger emotions, than others. The qualities which 'strike' or 'occupy' us come to the fore, crowding all others out. Ribot says: "Perception seeks to apprehend all the features of an object. But it fails, for an inner enemy frustrates this: the innate eagerness of the mind for simplification, for elimination. The same horse in the same moment is not perceived in the same way by a horse-vendor, a veterinarian, a painter and an uninterested man. In the mind of each, certain features, for each different, stand out; others are pushed back. There is always some inadvertent choice of main features which, taken together, replace the whole. For perception is first of all a practical activity, directed in the first line by what wakes our interest or serves our advantage; thus we neglect, leave half-conscious, whatever wakes no interest and yields no advantage" (30).
   It is not perceptual imagery of physical objects alone which is subjected to this law, which Ribot calls loi d'intérêt, but also imagery of mental objects. The best examples stem from cases where mental states consisting of impressions connected to emotions are objects of perceptual imagery ­ as, for example, of a toothache. When we perceive such imagery, we pay no heed to the sensory impressions which constitute the pain; in consciousness, only the pain appears vividly. Of the two features of our mental state, impressions and emotions, only the latter arrest the attention. Only by exactly realizing the imagery content corresponding to this mental state do we ascertain that we are aware, not only of pain, but also of impressions located in the tooth ('drilling', 'jerking'). Thus, the imagery of the mental state entails both features, but highlights one at the expense of the other. All perceptual imagery for mental objects is similarly affected.
   Unequal attention to individual features in imagined objects arises not only in perceptual imagery, but also in reproductive and creative imagery. The same motives come into play (loi d'intérêt) in each case. One can say that no imagery could give us all features of an imagined object with an equal degree of vividness. Some always come to the fore, others remain in the background; the difference may be very small, even negligible, but can always be discovered in closer analysis. This is easily established by creating a perceptual image in oneself, for example by looking at a book laying on a table. Then, as we close our eyes and reconstruct the imagery, we will notice that we remember well the colour of the book and its thickness, but do not recall whether it was lying with its edges parallel to the edges of the table. It means that this last feature (position) appeared less vividly in our perceptual imagery than did the other features.
   The property by which imagery brings out some features of imagined objects more vividly, others less vividly, may be called sketchiness. In ordinary life, we say we know things sketchily, that is in outline, without being able to account for details. Analogously, imagery does not present all the details of an object equally, but leaves the mind only the most striking or best remembered features. Our imagery is to ideal imagery, which would contain all the features of an imagined object, as is a sketch to a finished painting.
   Sketchiness is then a third feature common to imagery, besides manifestness and concreteness. Some suggest singularity as a further property of imagery; this would consist in imagery's referring only to one object, as opposed to general concepts, referring to artificial or natural groups of objects. We cannot, however, accept this view; on the contrary, one can show that imagery need not necessarily be singular and can be, and often is, general.

8. The scope of imagery

   Let us suppose we have perceptual imagery of an object P, with the features a, b, c, d, e..., which we designate by a formula P1 = f1(a,b,c,d,e...). Some of these, as we show above, here b and c, are cast in our minds more vividly than others; these are marked by differently shaped letters in the corresponding formula. Let us further suppose that this perceptual imagery is followed in our mind by another, e.g. P2 = f2(a,c,d,m,n...), and then a third P3 = f3(r,c,d,s...), a fourth P4 = f4(g,c,d,w,z), etc.
   First, we note that one feature, represented as c, recurs in each imagery, always attracting our attention. Secondly, another feature d reappears in each but always stands aside. Thirdly, yet another feature a also recurs sometimes, at times appearing clearly (P2), at times pushed back. Fourth and finally, each of the other features (e,m,n,s,w,z,g) appears only once. Of course, the arrangement above, as an example, could be replaced by any other. Yet whenever features reappear in successive perceptual imagery, and especially when they immediately attract our attention, these features consequently dominate our memory above all others. Thus, in the reproductive imageries corresponding to the four perceptual imageries given above, the feature c will come to the fore; the feature d will also appear clearly, as repetition has fixed both in the memory. All other features will appear somehow hazy, as mutually effacing and displacing each other in memory.
   Thus, the reproductive imagery here could be presented as follows: p1 = f1(c,d,a,b,e,), p2 = f2(c,d,a,m,n...), p3 = f3(c,d,r,s,..), p4 = f4(c,d,g,w,z,..). Since in each of these we clearly realize only c and d, not attending to the other features, that which occupies our mind ceases to matter in the course of thinking. Unless we attend to the features in which they differ, we do not differentiate among the four. Thus, each can serve as reproductive imagery for the first, second, third or fourth perceptual imagery. For if we reconstruct in each case mainly c and d, and all the other features only indistinctly, each reproductive imagery resembles the features common to all the perceptual imageries, omitting those in which they differ.
   This state of affairs is susceptible to two interpretations; the perceptual imageries which founded the reproductive imagery either stemmed all from one object, or from a few similar objects.
   In the first case, an object was perceived several times, undergoing changes between each perception: for example, we see a person well known to us in different situations or in different clothes. Recalling this person in memory, we note that the reproductive imagery which appears in the mind gives the face precisely, but brings neither a particular place nor the colour or fashion of particular clothes to mind. Clearly we imagine this person somewhere, dressed somehow, but these data give merely a background, none too clear, on which the face quite clearly appears. Moreover, this background may be changed; at any moment other environments or clothes can come to mind, yet the features of the face remain unchanged. It is impossible to determine where the reproductive imagery now in our mind originated, from which of the many perceptual imageries directed toward this person. In fact, it does not matter; wherever it originated, it fulfills its appointed task: it makes us realize the object's enduring, rather than its changeable, features.
   In the second case, reproductive imagery has a quite different sense, as it stems from perceptual imagery drawn from different but similar objects. In this case, the mental state is as before, but the role of imagery is different. For example, someone comes for the first time into the company of many people of another race quite different from ours, let us say Negroes. He will have the impression that all the individuals of this race were alike. This is due to the sketchiness of imagery. When we perceive a Negro, the features which are most striking to us come to the fore: black skin, thick lips, etc; other features, particularly the face, appear in perceptual imagery so unclear that in comparison with the former they disappear, as it were.
   One sees in any case that all perceptual imagery is quite sketchy. As such, images appear in great numbers, in succession and in accord with reproductive trailing after previous perceptual imagery in certain features. These features are inculcated more and more into memory at the expense of others, different in each imagery. Finally, we cannot realize the differences obtaining between individual imageries. When we recall a Negro to mind, we create reproductive imagery in our mind which could be a reconstruction of any perceptual imagery of a Negro, since it presents vividly only those features strongly marked in each perceptual imagery. Yet these will not be permanent features of one object undergoing change over the course of time, but features common to several different objects. Thus, our mind will possess reproductive imagery which refers, not to this or that individual object, but in referring to any one, encompasses all.
   Can we consider such imagery singular? It does not fulfil the essential condition that singular imagery refers only to one object. Moreover, we can make general statements on the basis of such imagery ­ statements which can be imprecise or even mistaken, but which doubtless belong to the category of general statements, and can even be true. [...] Such statements constitute significant proof that the imagery to which they refer is not singular.
   One could argue that we are not dealing with imagery here, but with general concepts. Those reluctant to relinquish the thesis that as such it is singular, will be inclined to endorse this view. Yet there is a ground which bars us from treating the phenomena above as general concepts.
   Even when we present a series of objects to ourselves sketchily, so sketchily that we do not realize the features with respect to which individuals differ, we always present these objects in a concrete and manifest way. As we have explained, the concreteness of imagery consists in the particularly compact integration and unification of its composite elements; it is marked by the lack of differentiation among these elements, on the part of the imagery subject. We may find cases where we present an object in general terms, recalling mainly the features it has in common with other objects, and despite this be unable to distinguish the elements making up this presentation. If so, we must admit this imagery to be concrete.
   It is not difficult to find examples for such cases. For example, one who heard different sounds made by violins will be able to recognize violins, distinguishing them from trumpets, pianos, etc. Thus, he is able to reconstruct in his memory not only the sound of some particular violin, but also violin sounds as such. Despite this, he cannot distinguish the elements common to violin sounds, from those in which violin sounds differ from those of other music instruments. Each sound is presented to his mind as something simple, since its elements (basic and harmonic tone) and the audible impressions corresponding thereto become integrated into one homogenous whole; distinguishing them is a special skill. Analogously, we recognize that the surface of a table which we touch is rough. Doubtless, we have the skill of presenting to ourselves roughness in general, though we do not distinguish the elements common to rough objects in which they differ from smooth ones. This is not otherwise in the sphere of colours.
   In all these cases, we imagine a violin sound, smooth surface, red colour, etc. such that we do not realize how the sound of one violin differs from that of another, one smooth surface from another, or one red swatch from others of the same colour. Yet we remember what these sounds, surfaces and colours have in common, even if we cannot realize the common elements, i.e. we cannot isolate them among others which together make up a concrete structure of imagery. There is no doubt that if we imagine a violin sound as described, i.e. in general terms, we imagine it concretely. Thus, we have imagery, though it refers to no object in particular, but comprises uniformly a number of objects similar in certain respects.
   We must admit such presentation as manifest, if only because concreteness and manifestness always come paired. Taken separately, manifestness can be completely consistent with objects presented such that only common features appear clearly, while individual features are more or less omitted. Imagery is manifest, so far as we present therein objects either based on real perception, or at least as they would appear in perceptual or reproductive imageries, were these possible and accessible to us. Sketchiness does not conflict with manifestness; indeed, this is how features common to multiple objects, dominate in consciousness over individual features. We must remember, however, that even in perceptual imageries the former might peremptorily dominate over the latter, as it were shouting them down.
   Coming back to our earlier example: say we hear the sound of a violin. The imagery of this sound doubtless embraces a number of individual features of a sound heard in a certain moment, in a certain environment. Yet when we listen intently, we do not realize such individual features of place and time. To uncover the individual features of a certain sound, one must be gifted in music and highly experienced; only such a person can notice what is peculiar to the sound of a certain violin, or recognize its sound among others. Even in perceptual imagery, individual features disappear from consciousness in favour of common features, though perceptual imagery is manifest all the while.
   Being concrete and manifest, sketchy imagery has not ceased to be real imagery, though it bring out clearly and definitively only features common to a certain number of objects. In this case it is not singular i.e. particular, since it refers not to one well-determined object, but to any object whose features are clearly highlighted by the imagery. Such imagery must then be general ­ no contradiction in adiecto, as Raciborski thinks (31). Modern psychology has grown so accustomed to general imagery as to introduce special technical terms for such imagery: Allgemeinbilder, generic imagining, imaginings génériques, as opposed to general concepts: Allgemeinbegriffe, general notions, notions (idées) générales.
   The generality of imageries stems from their sketchiness; yet while all imagery is sketchy, not all is general. On the contrary: a great deal of imagery is (as all imagery) sketchy, but at once singular. This comes whenever an imagery shows vividly the individual features of an object imagined (as the features of a certain face). Only where individual features escape our attention, has imagery become general.
   Summarizing our consideration, we can derive the following definition: in general imagery, the individual features of an imagined object escape the attention of the imagery subject. We see that this distinguishing quality of imagery is not at all necessary for general concepts, constituting a new proof that general imagery exists apart from general concepts.
   As not all imageries have the same scope, we cannot characterize imagery in this respect; we must be satisfied with the features of concreteness, manifestness and sketchiness. These are absolutely sufficient to distinguish imageries from concepts.

[Translated by Agnieszka Lekka-Kowalik]

[Brentano 1867] F. Brentano, Die Psychologie des Aristoteles, Mainz, F. Kirchheim; English edition [Brentano 1977].

[Brentano 1977] F. Brentano, The psychology of Aristotle, ed. and transl. by R. George, Berkeley, Berkeley Univ. Press.

[Descartes 1970] R. Descartes, Philosophical writings, transl. by E. Anscombe, P.T. Geach, London, Nelson Univ. Paperbacks for Open University [new edition 1993].

[Erdmann 1886] J.E. Erdmann, "Zur Theorie der Apperzeption" Vierteljahrsschrift für wissenschaftliche Philosophie 10.

[Höfler 1897] A. Höfler, Psychologie, Wien ­ Prague, F. Tempsky.

[Hume 1895] D. Hume, Traktat über die menschliche Natur, ed. by Th. Lipps [Leipzig, L. Voss]; Engl. edition [Hume 1960].

[Hume 1960] D. Hume, A treatise of human nature, vol. 1, London, Dent.

[Jodl 1886] F. Jodl, Lehrbuch der Psychologie, Stuttgart, J.G. Cotta.

[Kerry 1885] B. Kerry, "Über Anschauung und ihre psychische Verarbeitung" Vierteljahrsschrift für wissenschaftliche Philosophie, 9.

[Marty 1890] A. Marty, "Über Sprachreflex, Nativismus und absichtliche Sprachbildung" Vierteljahrsschrift für wissenschaftliche Philosophie 14; repr. in [Marty 1916].

[Marty 1916] A. Marty, Gesammelte Schriften, ed. by J. Eisenmeier, A. Kastil, O. Kraus, Halle, M. Niemayer.

[Meinong 1889] A. Meinong, "Phantasievorstellung und Phantasie", Zeitschrift für philosophische Kritik, 95, 161-244; repr. in [Meinong 1969], 193-271.

[Meinong 1969] A. Meinong, Gesamtausgabe, vol. 1., Abhandlungen zur Psychologie, ed. by R. Kindinger, R. Haller, Graz, Akademische Druck und Verlangsanstallt.

[Mill 1865] J.St. Mill, Collected works, London, Longmans; new edition [Mill 1979].

[Mill 1979] J.St. Mill, Collected works, Toronto, Toronto Univ. Press.

[Raciborski 1886] A. Raciborski, Podstawy teorii poznania w 'Systemie logiki indukcyjnej i dedukcyjnej J.St. Milla' [The foundations of the theory of cognition in J.St. Mill's 'System of inductive and deductive logic'].

[Ribot 1897] T. Ribot, L'évolution des idées générales, Paris.

[Rickert 1888] H. Rickert, "Zur Lehre von der Definition".

[Rickert 1894] H.Rickert, "Zur Theorie der naturwissenschaftliche Begriffsbildung", Vierteljahrsschrift für wissenschaftliche Philosophie 18.

[Schmitz-Dumont 1881] Schmitz-Dumont, "Die Kategorien der Begriffe", Vierteljahrsschrift für wissenschaftliche Philosophie 5.

[Schopenhauer 1813] A. Schopenhauer, Über die vielfache Wurzel des Satzes vom zureichenden Grunde [Dissertation], Leipzig.

[Scripture 1892] E.W. Scripture, "Zur Definition einer Vorstellung", Philosophische Studien 7.

[Sigwart 1889] Ch. Sigwart, Logik, Freiburg, Mohr, vol 1., 2nd edition.

[Struve 1896] H. Struve, Wstep krytyczny do filozofii [Critical introduction to philosophy] .

[Sully 1884] J. Sully, Outlines of psychology, London, Longman.

[Taine 1885] H.A. Taine, De l'intelligence, Paris, Hachette, 5th edition.

[Twardowski 1894] K. Twardowski, Zur Lehre vom Inhalt und Gegenstand der Vorstellungen. Eine psychologische Untersuchung, Wien, Hölder; Englisch edition [Twardowski 1977].

[Twardowski 1897] K. Twardowski, "Psychologia wobec fizjologii i filozofii" [Psychology in relation to physiology and philosophy], Przeglad Naukowy i Literacki [Scientific and Literary Review]; repr. in [Twardowski 1965].

[Twardowski 1965] K. Twardowski, Wybrane pisma filozoficzne [Selected philosophical writings], Warszawa, PWN [Polish Scientific Publishers].

[Twardowski 1977] K. Twardowski, On the content and object of presentations. A psychological investigations, transl. and with an introd. by R. Grossmann, The Hague, M. Nijhoff.

[Wundt 1896] W. Wundt, Grundriss der Psychologie, Leipzig, W. Engelmann.

  Back to Twardowski's main page