A Short History of Modern Philosophy: From Descartes to Wittgenstein, Second Edition (6 page)

The first argument is ‘cosmological’ in that it starts from a premise about the actual world (the premise that I have an idea of God) and asks what caused that premise to be true. The more usual form of such an argument simply asks again and again what caused the world to be as it now is, until the question seems to demand the answer that there was a
first
cause, which has the property of being
‘causa sui’,
or explanation of itself. Hence the cosmological argument, as Kant points out in his famous critique of rational theology, will always require an ontological argument to support it, the ontological argument being simply the attempt to explain how it is that God can be
causa sui
(Critique of Pure Reason,
A.608). In Descartes the interdependence of the two arguments is shown succinctly in the scholastic principle, which he claims to derive from the natural light, that there must be at least as much reality in the cause as in the effect. This principle is vital for Descartes’ cosmological proof and also dependent upon the fundamental preconceptions of the ontological argument for its intelligibility.

Having, as he thinks, established the existence of God, Descartes goes on to draw his desired conclusions. First, that there is an objective world of which he, Descartes, is but a small, dependent and finite part. Secondly that, since God is all-perfect, he is no deceiver. From which it follows that those faculties that Descartes has innately will, when used in accordance with their true and God-given nature, lead him, not into error, but towards genuine discovery. In other words, the hypothesis of the evil genius can be dismissed, as can every other form of radical doubt. The existence of God guarantees those claims to knowledge which, by using his faculties to their greatest ability, Descartes will be naturally inclined to make.

Two difficulties arise at this point, and were already pointed out to Descartes in the series of objections collected by Mersenne (see p. 40). The first is, how does Descartes account for the possibility of error? If God is no deceiver, why does he permit error in any form? The second is this: if the existence of God is needed to guarantee the judgements about the world which we would, using our faculties to their best measure, instinctively arrive at, then do we not need to be assured of God’s existence before we can guarantee that the ‘clear and distinct’ perceptions whereby that existence is proven do really have the authority which they appear to have? In which case does not the validity of the argument for God’s existence covertly rely on the truth of its conclusion? In other words, is it not viciously circular? In answer to the first of these difficulties Descartes developed a complex theory of ‘assent’ to truth, a theory which assigns ‘assent’ to the will rather than the intellect. Ideas in themselves contain no error: but error is in us when we choose to assent to an idea that we do not clearly and distinctly perceive. Human error is therefore the necessary consequence of human freedom, and this seeming evil is part of a real and greater good.

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.

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.