In answer to the second difficulty—the so-called ‘Cartesian circle’— Descartes was apt to be impatient, and commentators do not agree as to the real nature of his reply. One theory is that Descartes held clear and distinct perception to be a guarantee of truth, so that the only error that could occur when working through an argument each step of which is clearly and distinctly perceived would be an error of memory. This error would be eliminated merely by rehearsing the proof at such length that it can be grasped in a single act of intellectual ‘intuition’. Even if this was Descartes’ reply, however, it has not satisfied many of his critics. Indeed, the Cartesian circle remains a major difficulty for the whole method of doubt. For if the evil genius really can deceive me in what I perceive most clearly and distinctly, then there is no hope of proving anything that is not self-verifying in the manner of ‘I exist’ and ‘I think’. I must then remain locked within my own subjective viewpoint, and deprived of all knowledge of an objective world. The difficulty is not one for Descartes only. All philosophical reasoning relies on principles that can be proved only by arguments that presuppose them. There is no point of view outside human reason from which reason can be judged. The nature of this difficulty, and the way in which it might be overcome, became clear only with Kant’s Critique of Pure Reason.
It is now necessary to return to the parts of Descartes’ philosophy for which he is chiefly remembered—his views concerning mind and matter on the one hand, and intellect and the senses on the other. It is on account of these views that we can now see Descartes as a founding force behind both the prevailing philosophies of the seventeenth and eighteenth centuries: rationalism and empiricism. Descartes’ view of matter is in fact closely bound up with his epistemology. In a famous passage of the Meditations he reflects roughly as follows: consider a lump of wax; it has a certain shape, size, colour, perfume. In short, it has certain qualities which I can perceive through the senses. It is tempting to say, therefore, that my senses reveal the nature of this lump of wax and tell me what it really is. But when I approach it to the fire I find that its colour, shape, hardness, perfume—in short, all those qualities in terms of which I might have sought to describe it and distinguish it from other things—undergo a change and may even disappear entirely. And yet it is the same piece of wax. It follows, Descartes thought, that it possesses its sensible qualities only accidentally—they are not ‘of its nature’ or ‘essential’.
Reflecting on this point Descartes came to the conclusion that not only are the senses intrinsically unreliable in discerning the reality of the physical world, but also that the real nature of physical objects must consist in something other than sensible qualities. These qualities simply constitute the passing mode in which the true physical essence clothes itself, and if we are to know that essence then we must consult, not the senses, but the intellect, which is alone capable of grasping the essences of things. What, then, is the essence of physical objects—what, as Descartes put it, is corporeal substance or body? The only properties that the wax seems to have essentially are extension in space, together with flexibility and changeability. In other words, material substance consists in extension (space) together with the various modes in and through which extension may change. This conclusion gives us the first principle of physical science, and Descartes was further confirmed in it by his reflections on geometry. These reflections had shown him that we really do have ‘clear and distinct’ perceptions of all the ideas of extension, and can reach knowledge of its properties through reason alone, by a deductive science that makes no reference to the sensible properties of things.
The argument, which I have very much abridged, was of considerable historical importance, being a direct precursor of Locke’s distinction between primary and secondary qualities (see chapter 7), and also the clearest statement in Descartes of the position that was later to be known as rationalism. Rationalism finds the key to knowledge, even of ‘sensible’ things, in rational reflection rather than in empirical observation. The argument about the wax shows that the distrust of the senses and the rationalist doctrine that there are knowable essences are intimately linked, and that together they go with a search for a priori principles of enquiry. Such principles will issue (like the axioms of geometry) in necessary, universal truths. As we shall see when we consider the philosophy of Leibniz, the difficulty for the rationalist is to explain the nature and possibility of contingent truths—of propositions which, while true, might have been false.
But while Descartes was, in this way, the founder of rationalism, there was another aspect to his philosophy which approached him more to later empiricists than to his immediate rationalist successors. This was the subordination of metaphysics to epistemology. Two consequences immediately stemmed from that. First, the conception of the first-person case as prior; secondly, the so-called Cartesian theory of the mind.
The priority of the first-person case follows from the Cartesian method. Descartes begins from the question ‘How can I know, be certain of, the things that I claim to know?’ Immediately his thought is turned inwards, to the contents of his own mind, and the specific certainties which attach to them. Although the peculiarity of the ‘cogito’ lies in its self-verifying nature, there lurks behind it a host of other certainties. These certainties we might call the certainties of ‘first-person privilege’. I am able to know what I think, feel, experience with an authority that is quite different from any authority that attaches to my knowledge of another person or thing. In the case of my own mentality, what is, seems, and what seems, is. The first-person case appears therefore to provide a paradigm of certainty, and from this certainty one may perhaps advance by degrees to a systematic vision of the world. While Descartes did not himself develop such a view of the ‘foundations’ of knowledge—relying as he did on a rationalistic argument for the existence of God, the premise of which was not first-person privilege as such but only the peculiar logical status of the ‘cogito’—he provided it with significant impetus. It is to later empiricism, however, that we must turn in order to find the view developed to its full.
The phenomenon of first-person privilege—variously described and explained—led directly to the Cartesian view of the mind. My immediate certainty of my own mental states is contrasted with my uncertainty about all corporeal things, in such a way as to lend support to the contention that what I am is an immaterial, substantial being, accidentally and temporarily connected with the body through which I act. I am a substance, but not a corporeal substance, and my privileged awareness of the contents of my own consciousness is supposed somehow to be explained by that. Descartes recognised that a difficulty must arise as to the mode of connection of mind and body: he proposed various half-formed and ultimately absurd hypotheses as to how this mental thing might interact with bodily substance, and his eminent failure to produce an explanation prompted Spinoza to provide a revolutionary account of how soul and body are related.
The Cartesian theory of mind has seemed obvious and compelling to philosophers throughout the centuries. Caricatured by Ryle as the view of mind as ‘the ghost in the machine’ (and despite Descartes’ claim that he is not lodged in his body like a pilot in a ship, he said little or nothing to prevent this caricature from remaining persuasive), it represents a deep illusion, generated by almost all epistemological thought. Epistemology usually assumes that it is from my own case that my knowledge derives, and that the certainty of self-awareness is to be explained only by the peculiar nature of the mind as an object of its own knowledge. One of the most impressive features of recent philosophy has been the demolition of this body of assumptions, and the consequent destruction of the dualistic vision of the world.
4 - THE CARTESIAN REVOLUTION
In the last chapter I gave some philosophical reasons in support of what is now the commonplace opinion that modern philosophy begins with Descartes. But there are further reasons for isolating him as the founder of philosophy in its modern form, reasons which are apt
to seem more pertinent to the historian of ideas than to the philosopher.
First, Descartes was not only a philosopher; he was also a great mathematician and a founder of modern physics. While it may now be usual practice to distinguish these subjects, this was not the common practice of Descartes’ time, nor would such practice have encouraged the development of any of them. Descartes belonged to that post-Reformation world in which, as the authority of Church and scripture receded, so did speculation and experiment advance. While almost all the philosophers and scientists of the time sincerely believed in the tenets of religion, they worked independently of its intellectual constraints, confident that by diligence alone they would establish the truth about matters which for centuries had remained in darkness.
It has been said of the scientific revolution of which Descartes was a part that
since [it] overturned the authority of the science not only of the Middle Ages but of the ancient world—since it ended not only in the eclipse of scholastic philosophy but in the destruction of Aristotelian physics— it outshines everything since the rise of Christianity and reduces the Renaissance and Reformation to the rank of mere episodes, mere internal displacements, within the system of mediaeval Christendom.
Sir Herbert Butterfield, Rise of Modern Science, p. vii.
And it is impossible to doubt now that the predilection of cultural historians to find the great divide between medieval and modern at the Renaissance has obscured and to some extent misrepresented the true development, not only of Western philosophy, but of Western thought as a whole. From ancient times until the mid-eighteenth century science and philosophy went hand in hand. For the historian of ideas, it is impossible to separate the development of philosophy from that of scientific thought, and, when taken together, it becomes apparent that the most significant point in the development of each occurred, not at the Renaissance, but in the early seventeenth century, in the intellectual turmoil that to some extent caused, and to a large extent was caused by, the thought of Descartes.
Already in the sixteenth century the problems of scientific method had been vigorously discussed—notably at the University of Padua, where it was recognised that experiments are of the first importance in scientific investigation, and also that experimental results can be fully understood only by a science of quantity and not by one of quality. Bacon had attempted to describe the form of such a science and the logic which would govern it, and such men as Harvey and Galileo had exemplified it in their writings and researches. But Descartes, partly because of his deep epistemological preoccupations, introduced with a novel explicitness the suggestion that there must be fundamental physical laws, of a kind so general as to provide the explanation of everything, and yet so abstract as to be the outcome not of experiment but of a priori reflection. He enunciated such laws in his Principles of Philosophy (1644), showing both their deductive dependence on metaphysics and their power to generate comprehensive explanations. Much of the content of the Principles was influenced by what Descartes had understood of the work of Galileo (whose comprehensive attack on the Aristotelian physics, the Dialogues of the Two Principal World Systems, was published in 1625-1629). But Descartes was perhaps the first to give clear prominence to the law of inertia. This law says that a body continues at rest or in motion in a straight line until something intervenes to halt, slacken or deflect its movement. The law makes movement into a basic fact of the physical universe, which may sometimes neither require nor permit further explanation. It reverses the traditional physics, which had postulated a ‘mover’ for every movement, believing motion as such to stand in need of an explanation. By accepting the law of inertia, and also embedding it at the heart of what he considered to be a rigorous, axiomatic system, Descartes changed the aspect of physical science and prepared the way for Newton.
However important Descartes’ contribution to science, he gave only a subordinate role to experiment, and a far more elevated role than would now be considered acceptable to metaphysical speculation. He wished to deduce the nature of the whole universe from the nature of God, with each step bound to its predecessor in an unbreakable chain of ‘geometrical’ reasoning. Everything was to be accounted for mathematically, either by configuration or by number, since mathematics gives us the most complete tabulation of ‘clear and distinct perceptions’ that we could ever hope to arrive at. No rival explanation therefore could compete with it. Any science that started from the mere evidence of the senses must be inferior in its conclusions to a science that began from principles so abstract that their persuasive power would be apparent to reason alone. It was not until Newton’s Principia (1687) that it was definitely established that the geometrical method could not prove the propositions of physics, and that it was only through a new, and previously unthought of, alliance of geometrical reasoning and experimental method that significant progress could be made. It is fair to say, however, that without Descartes Newtonian physics would have been impossible, and that since Descartes’ physics was the child of his philosophy there is a further historical reason for thinking that the Cartesian philosophy marks the birth of much that we would recognise as peculiarly ‘modern’ in the spirit of scientific investigation.
In philosophy itself the immediate impact of Descartes was enormous. The lucidity of his style, his contempt for scholastic technicalities, the clarity, honesty and unassuming objectivity of his approach, made it impossible to resist the appeal of his writings. Many of the greatest thinkers of the time felt called upon to respond to Descartes’ Meditations, offering their objections either directly to the author, or else indirectly, to the tireless impresario Father Marin Mersenne (1588-1648), who, with a humility remarkable in a man of less than total genius, acted as go-between among the scientists and philosophers of his age, achieving for the France of his day what the Royal Society was later to achieve for England. The objectors included Thomas Hobbes, Pierre Gassendi and the young priest Antoine Arnauld (1612-1694), who put forward the objection referred to in the previous chapter, arguing that Descartes’ proof for the existence of God must be circular. The interest of this objection lies in the suggestion that a search for method as absolute as Descartes’ must in the end rely not only upon ‘self-verifying’ truths such as the ‘cogito’, but also, and more generally, upon some characteristic of our mental processes whereby we recognise the intrinsic validity of ideas. The ‘clear and distinct perception’ of Descartes must itself be immune from Cartesian doubt. If this is so, then the faculty which governs clear and distinct perception, the ‘natural light’, of reason, is our ultimate guarantee of knowledge. It is in the recognition of this commitment that Cartesian rationalism is born, out of a sceptical epistemology that seemed at first to make rational enquiry as dubious as our other claims to knowledge.
Arnauld is significant not only as a critic of Descartes but also as expressing the spirit which arose, partly in opposition to Cartesian enlightenment and partly as its natural corollary, in the philosophy of Jansenism. Cornelius Jansen (1585-1638) was bishop of Ypres and an enthusiastic exponent of doctrines which, while seemingly compatible with the new findings of science, exalted the act of faith above the conclusions of reason as our guide to theological and metaphysical truth. He joined with the Abbé de Saint-Cyran in founding what is known as the Port-Royal movement, after the abbey where its activities were located. Arnauld was a member of this movement, and was associated with two decisive thinkers of the time: the moralist Pierre Nicole (1625-1695) and the famous mathematician and philosopher, Blaise Pascal. Together with Nicole, Arnauld wrote a textbook of logic for the Port-Royal School, under the title La Logique ou l’art de penser (1662), usually known as the Port-Royal logic. This work exemplifies the profundity of the Cartesian revolution in philosophy, and also anticipates the difficulties which the Cartesian ‘geometrical method’ was soon to encounter.
Judged from the historical point of view, the Port-Royal logic is merely one among a multitude of manuals designed to abbreviate
and restate a discipline that had become too deeply overlaid by the pernickety squabbles of the scholastics to recommend itself to the new man of science. In 1556, Petrus Ramus had published his Animadversiones Aristotelicae, in which he claimed to discredit the whole science of logic as Aristotle had invented and the scholastics embellished it. By the midseventeenth century faith in Aristotelianism was so much shaken that it seemed vital to achieve some rival logic with which to record and validate the ‘method’ of the new philosophy. In fact no systematic alternative to the Aristotelian logic was to emerge until the nineteenth century, and, despite many attempts (culminating in some notable ones from Leibniz), the seventeenth-century logic was less new than it claimed to be. It served partly to mask the old Aristotelian theories in Cartesian jargon. Without Aristotelian logic the rationalist conception of substance is, after all, scarcely intelligible; and yet it is this concept which lies at the heart of the philosophy of Descartes, Spinoza and Leibniz, surviving, in modified form, even in the works of Kant.
There are, however, important philosophical reasons for noticing the Port-Royal logic at this juncture. First, it represents an attempt to examine the nature of human reasoning in the light of the Cartesian theory of ideas. Traditional logic had spoken of the relations between judgements or propositions. It was unclear to Arnauld and Nicole how this logic bore on those more important relations without which there could be no such thing as the Cartesian ‘method’: the relations among ideas. The Cartesian ‘idea’, seeming to be both concept and proposition at once, has no claim to be the true subject matter of logic. As philosophers came to perceive this, so logic began again to make the progress which for centuries had been denied to it.
A Short History of Modern Philosophy: From Descartes to Wittgenstein, Second Edition Page 5