Descartes used the term “perception” (Latin perceptio, French perception) in several related ways. In the most general sense, expressed in a formal definition in the Principles of Philosophy, “perception” is any operation of the intellect (as contrasted with the will), comprising sensation or sense perception (sentire), imagination, and pure intellect or pure understanding (AT VIIIA 17, CSM I 204). In this general sense, to perceive is to be aware of or to grasp ideas or mental contents and perhaps, by virtue of such contents, to cognize mind-independent objects and their properties. Descartes applies this notion of perception to a variety of mental contents, including obscure and confused sensations, clear and distinct ideas (see clarity and distinctness), images in imagination, and purely intellectual ideas of extension, thought, and simple natures, as well as to principles such as “what is done cannot be undone” (AT VII 145, CSM II 104) and to everyday propositions, such as that wax is present or men are in the square. The latter act of perception is complex, involving the sensory experiences of human-shaped figures and the judgment that they are men (AT VII 32, CSM II 21).

For discovering and establishing the principles of Descartes’ metaphysics, the clear and distinct perceptions of the pure intellect are foundational. His Meditations can be read as preparing a reader hitherto immersed in sensory experience to enter a special kind of cognitive state: the perception of metaphysical truths concerning the essences of things (AT VII 9, 171–72, 178, 440–47; CSM II 8, 121, 126, 296–301). Building on the claim in the Second Meditation that he perceives the existence of a thing that thinks from the experience of doubt or other thoughts (the cogito reasoning), Descartes guides the reader to seek a purely intellectual apprehension of God in the Third and Fifth Meditations, an intellectual perception of extension and of geometrical essences in the Fifth and Sixth Meditations, and the clear and distinct perception of mind and body as distinct kinds of substance in the Sixth Meditation.

For these purposes, Descartes has the reader turn away from sense perception and imagination. He excludes sense perception as a first basis for metaphysics, ceding authority to the intellect in perceiving “the essential nature of bodies” (AT VII 83, CSM II 58).

Descartes used the term “nature” (Latin natura, French nature) with several meanings, each of which has some relation to previously established usage. The term “nature” might mean “nature in general,” which Descartes glossed as “God himself,” or “the coordination of created things instituted by God” (AT VII 80, Heffernan 199–201). Laws of nature belong here. In this usage, nature when taken as a whole is an ordered system, but it also consists in the “coordination” of individual kinds of thing, such as the human being as a composite of mind and body in which a system of relations has been established between brain states and sensations (see extrinsic denomination). Things “instituted” or “ordained” by nature belong here (AT VI 130, CSM I 167). Further, in this first sense a quality or ability may “naturally” belong to something, such as the natural light or the legitimate teachings of nature (AT VII 80–81, CSM I 56). In a second usage, “nature” is equivalent to essence. It serves as an abstract term for the principal attribute of a substance, the “nature and essence” of that substance (AT VIIIA 25, CSM I 210). Related notions include simple natures and true and immutable natures. There is a third usage that arises in Descartes’ philosophy because of his reorganization of finite substances into two kinds, mind and matter, which necessitated a replacement notion for substantial forms of the various natural kinds, a replacement that construes kinds of material things as possessing only properties permitted in an exclusively corporeal substance. This third notion concerns characteristics of material things stemming from their organization. The most extensive use of this notion occurs in the Principles of Philosophy, but is also frequently found in the Discourse on the Method, the Dioptrics, the Meteorology, The World (or Treatise on Light), and the Treatise on Man.

Descartes used the word “animal” (Latin animal, French animal) for animals in general, including human beings, and the term “beast” (Latin bestia or brutum, French bête) for nonhuman animals. He developed a new approach to nonhuman animals as mindless machines, lacking sentience. In line with the similarity between human and animal bodies (henceforth, “animal” means nonhuman animals), he treated the human body as a machine as well, albeit ensouled. Descartes recognized that animals behave so as to preserve their bodies in relation to environmental circumstances. His conception of animals as mere machines required that he explain such behavior using material mechanisms alone, in accordance with his doctrine that matter or body (corporeal substance) has extension as its essence, modified only by the properties of size, shape, position, and motion.

Discussion of animal cognition increased throughout the seventeenth century. Before Descartes’ animal machine hypothesis, debate was focused on whether animals reason. Michel de Montaigne famously argued that human and animal cognition do not differ in kind. Pierre Charron held a similar position, sparking a controversy that drew in Marin Cureau de la Chambre, whom Descartes knew in the 1640s, and Pierre Chanet. The latter two authors adhered to the received opinion among Scholastic Aristotelians (see Scholasticism) that the cognitive capacities of humans and animals differ in kind. These discussions included both natural history, describing animal behavior, and natural philosophy, seeking to explain those behaviors (Harrison 2004). Descartes focused on the latter, using few examples of animal behavior in his theoretical discussions. His followers, such as Antoine Le Grand, tested the animal-machine doctrine against the natural history literature.

Within the Aristotelian philosophy that Descartes knew well, all natural kinds, whether mineral, vegetable, or animal, were constituted by a substantial form inhering in matter. This “matter” was not conceived as a stand-alone substance and so is not Descartes’ bare extended corporeal substance. It serves as substrate for the substantial form, which is an active principle that directs the development of each kind of thing toward its characteristic properties. An acorn contains the form of the oak and, in growing, organizes its matter into an oak tree with branches and leaves. Animals, nonhuman and human, have their various substantial forms, with capacities that guide the animals’ behaviors in relation to environmental circumstances.

Throughout the eighteenth and nineteenth centuries, psychology was the study of the soul or mind, or, with greater ontological modesty, of mental powers, capacities, and phenomena. Insofar as these investigations concerned mind as substance and its relation to the body, they were metaphysical. Insofar as they concerned the cognitive abilities of the mind and the basis of and limits to human knowledge, they were epistemological (a term coined in the 1840s). Insofar as they concerned the description and explanation of various psychological phenomena, they were studies in empirical and theoretical psychology, which may be called scientific psychology, where “science” connotes empirical or natural science, that is, systematic knowledge based in observation or experience.

The quantitative experimental scientific psychology that became prominent by the turn of the twentieth century grew from three main areas of intellectual inquiry. First and most directly, it arose out of the traditional psychology of the philosophy curriculum, as expressed in theories of mind and cognition. Second, it adopted the attitudes of the new natural philosophy of the scientific revolution, attitudes of empirically driven causal analysis and exact observation and experimentation. Third, it drew upon investigations of the senses. Natural philosophical disciplines such as optics and acoustics treated the functioning of the senses. Optics, in particular, had from antiquity comprised a complete theory of vision, combining the physics, physiology, psychology, metaphysics, and epistemology of vision, using mathematical techniques where feasible. Within medicine, sensory physiology examined anatomy, physiology, and pathology. Philosophical psychology had long examined the senses as mental capacities connected with cognition and knowledge, and such discussions also heeded the new attitudes of natural philosophy.

Although the “Transcendental Aesthetic” is the briefest part of the first Critique, it has garnered a lion's share of discussion. This fact reflects the important implications that Kant drew from his arguments there. He used the arguments concerning space and time to display examples of synthetic a priori cognition, to secure his division between intuitions and concepts, and to support transcendental idealism. Earlier, in the years around 1770, Kant's investigations into space and time had facilitated his turn toward “critical” philosophy. Prior to that time, Kant's main interests in space and time pertained to physics and metaphysics. As he entered the critical period, he delved into the cognitive basis of our experience of space (and time), and drew his conclusions about their ideality.

Kant's doctrines of space and time provoked extensive response in his own time and throughout the nineteenth century. These responses variously concerned the metaphysics, physics, epistemology, psychology, and geometry of space. Throughout the nineteenth century, philosophers, physiologists, and psychologists sought to extend or to refute Kant's theories of space. By the last decades of the nineteenth century, many had rightly concluded that the existence of non-Euclidean geometry as a candidate description of physical space refuted Kant's full doctrine of space - though some have hoped that his position might be saved by restricting it to “visual space.”

Preface

These prolegomena are not for the use of apprentices, but of future teachers, and indeed are not to help them to organize the presentation of an already existing science, but to discover this science itself for the first time.

There are scholars for whom the history of philosophy (ancient as well as modern) is itself their philosophy; the present prolegomena have not been written for them. They must wait until those who endeavor to draw from the wellsprings of reason itself have finished their business, and then it will be their turn to bring news of these events to the world. Otherwise, in their opinion nothing can be said that has not already been said before; and in fact this opinion can stand for all time as an infallible prediction, for since the human understanding has wandered over countless subjects in various ways through many centuries, it can hardly fail that for anything new something old should be found that has some similarity with it.

My intention is to convince all of those who find it worth while to occupy themselves with metaphysics that it is unavoidably necessary to suspend their work for the present, to consider all that has happened until now as if it had not happened, and before all else to pose the question: “whether such a thing as metaphysics is even possible at all.”

The translation has been made using the original edition of the Prolegomena zu einer jeden künftigen Metaphysik die als Wissenschaft wird auftreten können (Riga, Hartknoch, 1783; reprint, Erlangen, Harald Fischer Verlag, 1988), and Karl Vorländer's edition, as revised (Hamburg, Felix Meiner Verlag, 1976); on occasion, Benno Erdmann's edition in Ak, vol. 4, has been consulted. As is customary, the page numbers of Ak are shown in the margins of the present translation. Vorländer's edition, completed after Ak, collects significant textual variants from many previous editions; both editions contain much useful information on texts and printings. Vorländer's edition incorporates a major reorganization of the Preamble and first General Question in accordance with Hans Vaihinger's “galley switching” thesis. Vaihinger convincingly argued, on internal textual grounds and by comparison with corresponding sections of the “B” edition of the Critique, that a galley of 100 lines was transposed during the printing of the Preamble. The emended text is not without minor problems (for the correction of which a paragraph break has been added), but it is much improved over editions that do not accept the reorganization.

The present translation varies slightly from my contribution to the Cambridge Edition, in Theoretical Philosophy After 1781. That publication contains more extensive critical apparatus than would be useful here, where the original German is given only occasionally, to permit a general understanding of Kant's terminology.

Preface to the Second Edition

Whether or not the cultivation of those cognitions that belong to the occupation of reason treads the sure path of a science can be assessed quickly from the results. If, after repeated preparations and provisions, this cultivation gets bogged down as soon as it reaches the goal, or if it must often backtrack and take another path to arrive at this goal; or equally, if it is not possible to unite the various collaborators on the manner in which their common aim should be pursued: then one can always be convinced that such a pursuit has not yet (by far) taken the sure path of science, but is merely groping about; and the discovery of this path, if possible, is already a service to reason, even if much should have to be abandoned as futile that was contained in the goal as previously accepted (without reflection).

That logic has tread this sure path from the most ancient times up to now can be seen from the fact that since Aristotle it has not had to take a single step backward, if the removal of a few superfluous subtleties or the clearer determination of what is presented are not to be reckoned as improvements, which anyway pertain more to the elegance than to the surety of the science.

The Göttingen Review

Critique of Pure Reason, by Immanuel Kant

1781. 856 p. Octavo

This work–which always exercises the understanding of its reader if not always instructing it, often strains the attention to exhaustion, occasionally comes to its aid with fortunate images or rewards it with unexpected, generally useful conclusions – is a system of higher, or, as the author calls it, transcendental idealism; an idealism that comprehends spirit and matter in the same way, transforms the world and our self into representations, and has all objects being generated from appearances, in that the understanding connects them into one experiential series and reason necessarily though vainly seeks to extend and unite them into one whole and complete world system. The author's system rests on approximately the following main principles. All our cognitions arise from certain modifications of our self that we call sensations. What they exist in, whence they are aroused, that is at bottom completely unknown to us. If there might be an actual thing in which the representations inhere, or actual things independent of us that produce them, we do not know even the lowliest predicate from the one or the other. All the same, we postulate objects; we speak of our self, we speak of bodies as real things, we believe we are acquainted with both, we make judgments about them. The cause of this is nothing other than the fact that the various appearances have something in common with one another.