The Rudolf Steiner Archive

7. Are There Limits to Cognition?

[ 1 ] We have established that the elements needed to explain reality are to be drawn from two spheres: perception and thought. As we have seen, our constitution dictates that full, total reality—including our own subject—appears to us initially as a duality. Cognition overcomes this duality by synthesizing the whole thing from the two elements of reality: perception and the concept derived through thought. Let us call the way in which the world presents itself to us, before it has taken on its proper form through cognition, the world of appearance, in contrast to the entity uniformly composed of perception and concept. Then we can say: The world is given to us as a duality (dualistic), and cognition processes it into a unity (monistic). A philosophy that proceeds from this basic principle can be called monistic philosophy or monism. Opposed to it is the theory of two worlds, or dualism. The latter does not assume two aspects of a unified reality that are merely distinguished by our organization, but rather two worlds that are absolutely distinct from one another. It then seeks explanatory principles for one world in the other.

[ 2 ] Dualism is based on a mistaken conception of what we call knowledge. It divides all of existence into two realms, each of which has its own laws, and places these realms in opposition to one another

[ 3 ] Such dualism gives rise to the distinction between the object of perception and the “thing-in-itself,” a distinction introduced into science by Kant and never since dispelled. According to our arguments, it is in the nature of our mental organization that a particular thing can only be given as perception. Thinking then overcomes this particularization by assigning each perception its lawful place within the totality of the world. As long as the separate parts of the totality of the world are determined as perceptions, we are simply following a law of our subjectivity in this separation. But if we regard the sum of all perceptions as one part and then set a second part against it in the “things-in-themselves,” we are philosophizing into thin air. We are then dealing with a mere play on concepts. We construct an artificial opposition, but cannot derive any content for the second member of the same, for such content can be drawn for a particular thing only from perception.

[ 4 ] Any form of being that is posited outside the realm of perception and concept must be relegated to the sphere of unwarranted hypotheses. The “thing-in-itself” belongs to this category. It is only natural that the dualist thinker cannot find a connection between the hypothetically assumed principle of the world and what is given by experience. For the hypothetical principle of the world, content can only be derived if one borrows it from the world of experience and deceives oneself about this fact. Otherwise, it remains a concept devoid of content, a non-concept that possesses only the form of a concept. The dualist thinker then usually claims: the content of this concept is inaccessible to our knowledge; we can only know that such content exists, not what exists. In both cases, overcoming dualism is impossible. If one introduces a few abstract elements from the world of experience into the concept of the thing-in-itself, it remains impossible to reduce the rich, concrete life of experience to a few properties that are themselves derived solely from this perception. Du Bois-Reymond believes that the imperceptible atoms of matter generate sensation and feeling through their position and motion, and then concludes: We can never arrive at a satisfactory explanation of how matter and motion produce sensation and feeling, for “it is simply and forever incomprehensible that a number of carbon, hydrogen, nitrogen, oxygen, etc., atoms should not be indifferent to how they lie and move, how they lay and moved, how they will lie and move. There is no way to understand how consciousness could arise from their interaction.” This conclusion is characteristic of the entire school of thought. From the rich world of perceptions, the following are isolated: position and motion. These are transferred to the imagined world of atoms. Then comes the astonishment that one cannot unwrap concrete life from this self-made principle borrowed from the world of perception.

[ 5 ] The fact that the dualist, who works with a concept of “in itself” that is completely devoid of content, cannot arrive at an explanation of the world follows directly from the definition of his principle given above.

[ 6 ] In any case, the dualist is compelled to impose insurmountable limits on our cognitive faculties. The adherent of a monistic worldview knows that everything he needs to explain a given phenomenon of the world must lie within the realm of the latter. The only things that prevent him from reaching this conclusion can be accidental temporal or spatial barriers or deficiencies in his own organization. And not human organization in general, but only his own particular individual organization.

[ 7 ] It follows from the concept of cognition, as we have defined it, that one cannot speak of limits to knowledge. Cognition is not a general matter of the world, but a task that human beings must undertake for themselves. Things do not require an explanation. They exist and interact with one another according to laws that can be discovered through thought. They exist in inseparable unity with these laws. Here our ego confronts them and initially grasps from them only what we have called perception. But within this ego lies the power to discover the other part of reality as well. Only when the ego has united the two elements of reality—which are inseparably linked in the world—within itself has the satisfaction of knowledge been achieved: the ego has returned to reality.

[ 8 ] The preconditions for the emergence of cognition are thus through and for the self. The latter sets itself the questions of cognition. Specifically, it derives them from the element of thought that is completely clear and transparent within itself. When we ask ourselves questions that we cannot answer, the content of the question cannot be clear and distinct in all its parts. It is not the world that poses the questions to us, but we ourselves who pose them.

[ 9 ] I can imagine that I have no way of answering a question I find written down somewhere without knowing the context from which the question is taken.

[ 10 ] Our understanding concerns questions posed to us by the fact that a sphere of perception—conditioned by place, time, and subjective organization—is set against a sphere of concepts that points to the totality of the world. My task consists in reconciling these two spheres, both of which are well known to me. There can be no talk of a limit to knowledge here. At any given time, this or that may remain unexplained because the circumstances of our lives prevent us from perceiving the factors at play. But what is not found today may be found tomorrow. The barriers resulting from this are only temporary and can be overcome with the advancement of perception and thought.

[ 11 ] Dualism commits the error of transferring the opposition between object and subject—which has meaning only within the realm of perception—to purely imaginary entities outside of it. But since the things distinguished within the horizon of perception are distinct only as long as the perceiver refrains from the thought that abolishes all distinction and reveals it as merely subjectively conditioned, the dualist transfers determinations to entities beyond perceptions that have no absolute, but only a relative validity even for those perceptions. In doing so, he breaks down the two factors relevant to the cognitive process—perception and concept—into four: 1. the object in itself; 2. the perception that the subject has of the object; 3. the subject; 4. the concept that relates the perception to the object in itself. The relationship between the object and the subject is a real one; the subject is truly (dynamically) influenced by the object. This real process is not to enter our consciousness. But it is to evoke in the subject a counteraction to the effect emanating from the object. The result of this counteraction is to be perception. This is what first enters consciousness. The object has an objective (subject-independent) reality, while perception has a subjective reality. This subjective reality relates the subject to the object. The latter relationship is an ideal one. Dualism thus divides the cognitive process into two parts. It allows one part—the generation of the object of perception from the “thing-in-itself”—to take place outside, and the other—the connection of perception with the concept and its relation to the object—to take place within consciousness. Under these conditions, it is clear that the dualist believes he can gain in his concepts only subjective representations of what lies before his consciousness. The objectively real process within the subject through which perception comes about, and all the more so the objective relations of the “things-in-themselves,” remain directly unknowable to such a dualist; in his view, human beings can only acquire conceptual representations of the objectively real. The bond of unity among things, which connects them to one another and objectively to our individual spirit (as a “thing-in-itself”), lies beyond consciousness in a being-in-itself, of which we could likewise have only a conceptual representation in our consciousness.

[ 12 ] Dualism believes it can reduce the entire world to an abstract conceptual framework unless it posits real connections alongside the conceptual relationships between objects. In other words: to the dualist, the ideal principles discoverable through thought seem too ethereal, and he seeks real principles upon which they can be grounded.

[ 13 ] Let us take a closer look at these principles of reality. The naive person (naive realist) regards the objects of external experience as realities. The fact that he can grasp these things with his hands and see them with his eyes serves as proof of their reality to him. “Nothing exists that cannot be perceived” can be regarded as the very first axiom of the naive person, which is just as readily accepted in its inverse form: “Everything that can be perceived exists.” The best proof of this assertion is the naive person’s belief in immortality and ghosts. He has a mental image of the soul as a fine, sensory matter that, under special conditions, can even become visible to the ordinary person (naive belief in ghosts).

[ 14 ] To the naive realist, this world—as opposed to the real world—is anything but real; it is, in fact, the world of ideas, unreal, “merely ideal.” What we add to objects in our thoughts is merely a thought about things. Thought adds nothing real to perception.

[ 15 ] But the naive person regards sensory perception as the sole evidence of reality not only with regard to the existence of things, but also with regard to events. In his view, one thing can only affect another if a force perceptible to the senses emanates from the former and seizes the latter. Early physics believed that very fine substances emanate from bodies and penetrate the soul through our sensory organs. The actual perception of these substances is impossible only because of the coarseness of our senses in relation to the fineness of these substances. In principle, these substances were acknowledged as real for the same reason that objects in the sensory world are acknowledged as real, namely because of their form of being, which was conceived as analogous to that of sensory reality.

[ 16 ] To the naive mind, the self-contained essence of what can be experienced ideally is not regarded as real in the same sense as what can be experienced sensually. An object conceived as a “mere idea” is regarded as a mere chimera until sensory perception can provide the conviction of its reality. To put it briefly, the naive person demands, in addition to the ideal testimony of his thinking, the real testimony of the senses. In this need of the naive person lies the basis for the emergence of primitive forms of revelatory faith. The God who is given through thought remains to the naive consciousness always only a “conceived” God. Naive consciousness demands manifestation through means accessible to sensory perception. God must appear in the flesh, and one attaches little importance to the testimony of thought, but only to the fact that divinity is demonstrated through the transformation of water into wine, which can be ascertained by the senses.

[ 17 ] Even the act of perception itself is imagined by the naive person as a process analogous to sensory processes. Things make an impression on the soul, or they send out images that penetrate through the senses, and so on.

[ 18 ] What the naive person can perceive with the senses, he considers to be real, and what he cannot perceive in this way (God, the soul, knowledge, etc.), he creates as a mental image that is analogous to what he does perceive.

[ 19 ] If naive realism seeks to establish a science, it can do so only by providing a precise description of the content of perception. For naive realism, concepts are merely a means to an end. They exist to create mental counterparts for perceptions. They mean nothing for the things themselves. For the naive realist, only the individual tulips that are seen, or can be seen, are considered real; the idea of the tulip is regarded as an abstraction, as the unreal mental image that the soul has constructed from the characteristics common to all tulips.

[ 20 ] Naive realism, with its principle that everything perceived is real, is refuted by experience, which teaches us that the content of perceptions is transient. The tulip I see is real today; in a year, it will have vanished into nothingness. What has endured is the genus tulip. For naive realism, however, this genus is “only” an idea, not reality. Thus, this worldview finds itself in the position of seeing its realities come and go, while what it considers unreal stands its ground against the real. Naive realism must therefore acknowledge not only perceptions but also something ideal. It must incorporate entities that it cannot perceive with the senses. It reconciles itself to this by conceiving their mode of existence as analogous to that of sensory objects. Such hypothetically assumed realities are the invisible forces through which things perceptible to the senses interact with one another. One such thing is heredity, which continues to act beyond the individual and is the reason why a new individual develops from the individual that is similar to it, thereby preserving the species. One such thing is the life principle permeating the organic body, the soul, for which one always finds in naive consciousness a concept formed by analogy with sensory realities, and is ultimately the divine essence of the naive human being. This divine essence is conceived in a way that corresponds entirely to what can be perceived as the mode of action of human beings themselves : anthropomorphically.

[ 21 ] Modern physics attributes sensory perceptions to processes occurring in the smallest parts of bodies and in an infinitely fine substance, the ether, or something similar. What we perceive as heat, for example, is the movement of the parts of the body that generates the heat within the space it occupies. Here, too, something imperceptible is conceived by analogy with the perceptible. The sensory analogue of the concept of “body” in this sense is, for example, the interior of a space closed on all sides, in which elastic spheres move in all directions, colliding with one another, striking the walls and rebounding from them, and so on.

[ 22 ] Without such assumptions, the world would, for naive realism, disintegrate into a disjointed aggregate of perceptions with no mutual relationships, which do not coalesce into a single unity. It is clear, however, that naive realism can arrive at this assumption only through an inconsistency. If it wishes to remain true to its principle—that only what is perceived is real—then it must not assume anything real where it perceives nothing. The imperceptible forces acting from perceptible things are, in fact, unjustified hypotheses from the standpoint of naive realism. And because it knows of no other realities, it endows its hypothetical forces with perceptual content. It thus applies a form of being (perceptual existence) to a realm where it lacks the means that alone can make a statement about this form of being: sensory perception.

[ 23 ] This internally contradictory worldview leads to metaphysical realism. It posits, alongside perceptible reality, an imperceptible one, which it conceives of as analogous to the former. Metaphysical realism is therefore necessarily dualism.

[ 24 ] Where metaphysical realism perceives a relationship between perceptible things (approximation through movement, becoming aware of an objective reality, etc.), it posits a reality. However, it can only express the relationship it perceives through thought, not through perception. The ideal relationship is arbitrarily made to resemble the perceptible. Thus, for this school of thought, the real world is composed of perceptual objects, which are in a state of eternal becoming, appearing and disappearing, and of the imperceptible forces from which the perceptual objects are produced and which are the enduring elements.

[ 25 ] Metaphysical realism is a contradictory blend of naive realism and idealism. Its hypothetical forces are imperceptible entities with perceptual qualities. It has decided to acknowledge, in addition to the realm of the world—for whose mode of existence it has a means of knowledge in perception—another realm in which this means fails and which can only be determined through thought. However, it cannot at the same time resolve to recognize the form of being conveyed to it by thought—the concept (the idea)—as an equally valid factor alongside perception. If one wishes to avoid the contradiction of imperceptible perception, one must concede that for the relationships between perceptions mediated by thought, there is no other form of existence for us than that of the concept. The world presents itself as the sum of perceptions and their conceptual (ideal) relationships when one discards the unjustified element from metaphysical realism. Thus, metaphysical realism converges into a worldview that demands the principle of perceptibility for perception and the principle of thinkability for the relationships among perceptions. This worldview cannot accept a third realm of the world alongside the world of perception and the world of concepts, in which both principles—the so-called real principle and the ideal principle—are simultaneously valid.

[ 26 ] If metaphysical realism asserts that, in addition to the ideal relationship between the object of perception and its perceiving subject, there must also be a real relationship between the “thing-in-itself” of perception and the “thing-in-itself” of the perceiving subject (the so-called individual mind), this claim is based on the false assumption of a non-perceptible process of being analogous to the processes of the sensory world. Furthermore, when metaphysical realism states: I enter into a conscious-ideal relationship with my world of perception; but with the real world I can only enter into a dynamic (force) relationship—it commits no less the error already criticized. A relationship of forces can only be spoken of within the world of perception (the realm of the sense of touch), but not outside of it.

[ 27 ] We shall call the worldview described above—into which metaphysical realism ultimately flows when it sheds its contradictory elements—monism, because it unites one-sided realism with idealism into a higher unity.

[ 28 ] For naive realism, the real world is a sum of perceptual objects; for metaphysical realism, reality extends beyond perceptions to include imperceptible forces; monism replaces these forces with the ideal connections it derives through thought. Such connections, however, are the laws of nature. A law of nature is, after all, nothing other than the conceptual expression of the connection between certain perceptions.

[ 29 ] Monism is simply unable to look beyond perception and concepts to seek other principles for explaining reality. It knows that, throughout the entire realm of reality , there is no reason to do so. It sees in the world of perception, as it immediately presents itself to perception, a half-reality; in the union of this with the world of concepts, it finds full reality. The metaphysical realist may object to the adherent of monism: It may be that, for your constitution, your knowledge is complete in itself, that no link is missing; but you do not know how the world is reflected in an intelligence organized differently from your own. The monist’s reply will be: If there are intelligences other than human ones, if their perceptions take a different form than ours, then for me only that which reaches me from them through perception and concept has meaning. Through my perception—specifically, through this specific human perception—I am, as a subject, set in opposition to the object. The connection between things is thereby interrupted. The subject restores this connection through thought. In doing so, it has reintegrated itself into the whole of the world. Since it is only through our subject that this whole appears severed at the point between our perception and our concept, true knowledge is also given in the union of these two. For beings with a different perceptual world (for example, with twice the number of sense organs), the connection would appear severed at a different point, and its restoration would therefore also have to take a form specific to these beings. Only for naive and metaphysical realism, both of which see in the content of the soul merely an ideal representation of the world, does the question of the limits of cognition arise. For them, namely, what exists outside the subject is an Absolute, something resting in itself, and the content of the subject is an image of it that stands entirely outside this Absolute. The perfection of cognition depends on the greater or lesser similarity of the image to the absolute object. A being with fewer senses than humans will perceive less of the world, while one with more senses will perceive more. The former will therefore have a more imperfect cognition than the latter.

[ 30 ] For monism, the situation is different. The structure is determined by the organization of the perceiving being, where the unity of the world appears to be torn apart into subject and object. The object is not absolute, but only relative—relative to this particular subject. The bridging of this opposition can therefore only take place in the very specific way that is unique to the human subject. As soon as the self, which is separated from the world in perception, reintegrates into the context of the world through reflective thought, all further questions—which were merely a consequence of the separation—cease.

[ 31 ] A being of a different nature would possess a different kind of knowledge. Ours is sufficient to answer the questions raised by our own nature.

[ 32 ] Metaphysical realism must ask: By what means is that which is given as perception given; by what means is the subject affected?

[ 33 ] In monism, perception is determined by the subject. However, the subject also possesses, within thought, the means to suspend the determinacy that it has itself brought about.

[ 34 ] Metaphysical realism faces a further difficulty when it attempts to explain the similarity between the worldviews of different human individuals. It must ask itself: How is it that the worldview I construct from my subjectively determined perceptions and concepts is the same as the one another human individual constructs from the same two subjective factors? How can I even infer another person’s worldview from my own subjective one? Based on the fact that people get along with one another in practice, the metaphysical realist believes he can infer the similarity of their subjective worldviews. From the similarity of these worldviews, he then further infers the equality of the individual spirits underlying the individual human perceiving subjects or the “I in itself” underlying the subjects.

[ 35 ] This conclusion is thus one drawn from a set of effects regarding the nature of their underlying causes. Based on a sufficiently large number of cases, we believe we can recognize the facts in such a way that we know how the inferred causes will behave in other cases. We call such a conclusion an inductive conclusion. We will, however, be compelled to modify its results if something unexpected arises in a further observation, because the nature of the result is determined solely by the individual form of the observations that have taken place. This conditional knowledge of the causes is, however, entirely sufficient for practical life, asserts the metaphysical realist.

[ 36 ] Inductive reasoning is the methodological foundation of modern metaphysical realism. There was a time when people believed they could derive from concepts something that was no longer a concept. They believed they could discern from concepts the metaphysical real entities that metaphysical realism requires. This kind of philosophizing is now a thing of the past. Instead, however, one believes that from a sufficiently large number of facts of perception one can infer the character of the thing-in-itself that underlies these facts. Just as one used to believe one could unwrap the metaphysical from concepts, so today one believes one can unwrap it from perceptions. Since one has the concepts before one with transparent clarity, one believed one could also deduce the metaphysical from them with absolute certainty. Perceptions do not present themselves with the same transparent clarity. Each subsequent one presents itself somewhat differently from the similar preceding ones. Basically, therefore, what is deduced from the preceding is somewhat modified by each subsequent one. The form of the metaphysical that is thus obtained can therefore only be called relatively correct; it is subject to correction by future cases. Eduard von Hartmann’s metaphysics bears a character determined by this methodological principle; he placed the following motto on the title page of his first major work: “Speculative Results According to the Inductive Scientific Method.”

[ 37 ] The form that the metaphysical realist currently ascribes to things-in-themselves is one derived from inductive inferences. He is convinced, through reflections on the process of cognition, of the existence of an objectively real structure of the world alongside the “subjective” one that is recognizable through perception and concepts. He believes he can determine the nature of this objective reality through inductive inferences drawn from his perceptions.

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Addendum to the New Edition (1918)

[ 38 ] For the unbiased observation of experience in perception and concept, as has been attempted to be described in the preceding remarks, certain mental images arising from the study of nature will repeatedly prove to be a hindrance. Standing on this ground, one tells oneself that through the eye, colors ranging from red to violet are perceived in the light spectrum. But beyond violet, in the radiation space of the spectrum, there are forces to which no color perception of the eye corresponds, though a chemical effect does; likewise, beyond the limit of red’s effectiveness, there are radiations that have only thermal effects. Through reflections directed at such and similar phenomena, one arrives at the view that the scope of the human world of perception is determined by the scope of human senses, and that one would have a completely different world before one’s eyes if one had other senses in addition to one’s own, or if one had any other senses at all. Anyone who indulges in the extravagant fantasies to which, in this vein, the brilliant discoveries of modern natural science in particular offer a rather seductive incentive, may well come to the conclusion: Only that which is capable of acting upon the senses shaped by human organization falls within the field of human observation. He has no right to regard this perceived reality, limited by his own constitution, as in any way authoritative for reality. Every new sense would present him with a different picture of reality. — All of this, considered within the appropriate limits, is a thoroughly justified opinion. But if anyone allows this opinion to mislead them in the unbiased observation of the relationship between perception and concept as asserted in these remarks, they block their own path to a world rooted in reality and to knowledge of humanity. The experience of the essence of thinking—that is, the active development of the world of concepts—is something entirely different from the experience of the perceptible through the senses. Whatever other senses a person might possess: none would provide him with reality unless he interwove the perceived, as mediated through it, with concepts through thinking; and every sense, whatever its nature, when thus interwoven, gives a person the possibility of living within reality. The question of how a person stands in the real world has nothing to do with the imagination’s conception of a potentially entirely different perceptual image through other senses. One must simply recognize that every perceptual image derives its form from the organization of the perceiving being, but that the perceptual image interwoven with the experienced, thinking contemplation leads a person into reality. It is not the fanciful imagination of how a world must look different to senses other than the human ones that can prompt a person to seek knowledge about their relationship to the world, but rather the insight that every perception provides only a part of the reality contained within it, that it thus leads away from its own reality. This insight is then accompanied by the further realization that thinking leads into the part of reality that is hidden from perception by perception itself. The unimpeded observation of the relationship between perception and the concept developed through thinking, as presented here, can also be disrupted when, in the realm of physical experience, it becomes necessary to speak not at all of immediately perceptible elements, but of abstract quantities such as electric or magnetic lines of force and so on. It may seem as though the elements of reality of which physics speaks have nothing to do with either the perceptible or the concept developed through active thinking. Yet such an opinion would be based on self-deception. First and foremost, it is essential that everything developed in physics—insofar as it does not constitute unjustified hypotheses that should be ruled out—is derived from perception and concepts. What appears to be abstract content is, by virtue of the physicist’s sound cognitive instinct, fully situated within the realm of perception, and it is conceived in terms used within that realm. The intensities of force in the electric and magnetic fields and so on are, in essence, not obtained through any cognitive process other than that which takes place between perception and concept. — An increase or transformation of the human senses would yield a different perceptual image, an enrichment or transformation of human experience; but true knowledge would also have to be gained from this experience through the interaction of concept and perception. The deepening of knowledge depends on the powers of intuition that unfold in thought (see page 95). This intuition can, in the experience that unfolds in thought, plunge into deeper or less deep strata of reality. Through the expansion of the picture of perception, this plunging can receive stimuli and be indirectly fostered in this way. However, never should this delving into the depths—as the attainment of reality—be confused with the contrast between broader or narrower fields of perception, in which always only a half-reality, as conditioned by the perceiving organism, is present. Whoever does not lose themselves in abstractions will realize how the fact that, for physics within the field of perception, elements must be unlocked for which no sense is immediately attuned—as is the case with color or sound—also comes into play for the understanding of the human being. The concrete nature of the human being is determined not only by what he confronts as immediate perception through his organism, but also by the fact that he excludes other things from this immediate perception. Just as the unconscious state of sleep is necessary to life alongside the conscious waking state, so too is a sphere—indeed, a much larger one—of elements not perceptible to the senses necessary to human self-experience alongside the sphere of sensory perception, within the field from which sensory perceptions originate. All of this has already been indirectly expressed in the original presentation of this text. The author adds this expansion of the content here because he has found that some readers have not read carefully enough. — It should also be borne in mind that the idea of perception, as developed in this treatise, must not be confused with that of external sensory perception, which is only a special case of it. It will be seen from what has already been said, but even more so from what is discussed later, that here everything approaching human beings in a sensory and spiritual sense is understood as perception before it is grasped by the actively formed concept. To have perceptions of a psychological or spiritual nature, senses of the commonly understood kind are not necessary. One might say that such an extension of ordinary linguistic usage is impermissible. Yet it is absolutely necessary if one does not wish to be constrained in the expansion of knowledge in certain areas precisely by linguistic usage. Whoever speaks of perception only in the sense of sensory perception will not, even through this sensory perception, arrive at a concept useful for knowledge. One must sometimes expand a concept so that it acquires its proper meaning within a narrower field. One must also occasionally add something to what is initially conceived in a concept, so that what is thus conceived finds its justification or even correction. Thus, on page 107 of this book, it is stated: “The mental image is therefore an individualized concept.” In response to this, it was objected to me that this is an unusual use of language. But this use of language is necessary if one wishes to get to the bottom of what a mental image actually is. What would become of the progress of knowledge if one were to object to everyone who is compelled to correct concepts by saying: “That is an unusual use of language.”