A Short History of Modern Philosophy: From Descartes to Wittgenstein, Second Edition (5 page)

But before Bacon’s influence could be widely felt, philosophy had undergone a radical convulsion. This was induced by Descartes’ declaration that all of philosophy’s results were without foundation until its premises could be agreed, together with a method whereby to advance from them. Only in the wake of Cartesianism was the nature of Bacon’s thought fully to be appreciated, and by then the disputes of scholasticism seemed irrevocably distant.

René Descartes (1596-1650), the principal founding father of modern philosophy, and well known as a mathematician, deserves the eminent place accorded to him on two accounts. First, because of his single-minded search for method in all branches of human enquiry; secondly, because he introduced into philosophy, largely on account of that search, many of the concepts and arguments which have since served as its foundation.

A contemporary of Bacon and Galileo, and immediate predecessor of Newton (many of whose thoughts he anticipated), Descartes was a perfect representative of the new scientific spirit. While he feared and respected the censure of the Church (as is shown by his withholding from publication the
Treatise on the Universe,
1633, upon hearing of Galileo’s condemnation), he deferred to no intellectual authority other than the ‘natural light’ of reason. This set him apart both from the scholastic traditions to which we have referred and also from the worldly preoccupations of the Renaissance humanists. For Descartes the results of all previous speculation had to be set aside or suspended, until clear and indubitable principles could be established against which to measure them. Without the aid of such principles, no system, scientific or metaphysical, could warrant assent. Descartes could not find these basic principles in the works that he had read. He therefore embarked on a programme of radical intellectual reform, which resulted in a change of philosophical perspective so great that scholasticism fell into lasting disrepute. Even now medieval philosophy is rarely studied in our universities and yet more rarely understood.

Descartes’ first important work was the
Discourse on Method
(1637), written in French in a style of remarkable elegance and distinction. In this book Descartes sets forth his life’s aim of directing his reason to the systematic discovery of truth and the elimination of error. The
Discourse
was followed by Descartes’ masterpiece, the
Meditations of First Philosophy,
published in Latin in 1641, which was soon followed by sets of objections from various writers together with Descartes’ replies to them. His other major philosophical works were
The Principles of Philosophy
(1644) and
The Passions of the Soul
(1649), the first being an ambitious attempt to systematise his philosophical method and derive from it foundations for an account of the physical world. The second was an exploration in the philosophy of mind which, while of considerable interest in itself, cannot be treated in what follows.

It is true to say that, despite the enormous influence of experimental science, the distinction between science and philosophy was not clear to the philosophers of Descartes’ day. Descartes himself—despite great expertise in physics and genuine mathematical genius—was slow to appreciate the difference. However, he came to believe that, as he put it, human knowledge is a tree, the trunk of which is physics, and the root of which is metaphysics. It is only through the exploration of metaphysics that the basis of human knowledge can be discerned. And ‘for right philosophising.the greatest care must be taken not to admit anything as true which we cannot prove to be true.’ We must therefore adopt a ‘method of doubt’, in order to arrive at propositions which could not be reasonably doubted.

Two arguments persuaded Descartes that he could doubt virtually all his normal beliefs. The first is the argument from dreaming. I believe that I am sitting by the fire with a piece of paper in my hand. Why? Because my senses tell me so. But could I not be dreaming? In dreams my senses present me with information of the same kind as I receive waking. So how do I know that I am not dreaming now?

There are beliefs which are not shaken by the argument from dreaming—beliefs about what is most general, such as we encounter in mathematics. ‘Whether I am awake or asleep,’ Descartes writes in the first Meditation, ‘two and three added together are five, and a square has no more than four sides.’ He therefore asks us to imagine a spirit of such power and such malignity, as to cause in me all the experiences that I have, and all the beliefs that are associated with them, with the express intention of deceiving me about both. What assurance have I that this ‘evil genius’ is not the real cause of my present beliefs and experience? It is useless to reply that the hypothesis is highly improbable. In the abstract, with no certainties to rely upon, I can have no grounds for knowing what is probable and what is not. My own experience, since it is equally well explained by common-sense beliefs about an external world and by the hypothesis of an evil genius, gives no grounds for choosing between them. Descartes even admits (see, for example,
Principles,
1, 5, 6) that the evil genius might be deceiving me ‘in those matters which seem to us supremely evident’, such as mathematics—an admission that threatens his own solution to these sceptical problems.

Descartes drew the conclusion that he could begin from no premise except those which he could not doubt. Metaphysics must begin from truths that are not just evident, but in some sense self-verifying: otherwise it will never be more than a shot in the dark. He went on to identify such a truth, arguing that ‘from the mere fact that I thought of doubting the truth of other things, it followed quite evidently and certainly that I existed’
(Discourse on Method,
32)—in other words, ‘I think, therefore I am’ (‘
Cogito ergo sum’).
This original statement of Descartes’ master-premise has given rise to the mistaken impression that the
cogito
is some kind of inference. In the
Meditations,
however, he corrects that impression: ‘the proposition
I am, I exist
is necessarily true whenever it is put forward by me or conceived in my mind.’ In other words, the proposition that I exist is self-verifying. I cannot assert it or think it without its being true. Likewise the proposition that I do not exist is self-defeating: to assert it is to give conclusive grounds for its disproof.

A similar argument can be mounted for the proposition that I think, which verifies itself in the very act of being doubted. Neither ‘I think’ nor ‘I exist’ expresses a necessary truth: each might have been false. Nevertheless, whenever they are true, I know for certain that they are true. My philosophy can begin from two indubitable premises which also express contingent and substantial truths about the world.

We should say that the truth that I exist is self-evident. Descartes wrote rather that it is manifest to the ‘natural light’ of reason. In other words, it is known by a process that can be perceived to be valid by anyone who reasons at all. The existence of this ‘natural light’ is not so much an arbitrary assumption as a precondition of all philosophical argument. There must be some point at which reason simply
finds manifest
the validity of an argument or the truth of an idea. Otherwise the process of reasoning itself will be thrown in doubt, and absolute scepticism will ensue. Without some reliance on reason, neither scepticism nor its opposite can be proven. Absolute intellectual darkness is the result. It is clear that Descartes in no way intended his method of radical doubt to bring about absolute scepticism; indeed he would have rightly regarded such scepticism as incoherent.

But what is the point at which the truth of an idea or the validity of an argument are revealed to reason? This question is one of the basic questions of philosophy. It is the question of the nature and limits of what has come to be known as
a priori
knowledge. The prime example of such knowledge for Descartes (who did not use the term
‘a prior
i’) is knowledge of the validity of a step in an argument. For example, I can see that from the proposition ‘p and q’ it follows that p. By way of explaining this as a basic operation of the natural light, Descartes would say that the relation between ‘p and q’ and ‘p’ is something that I perceive clearly and distinctly. Anything that I perceive clearly and distinctly is something the truth of which I can discern without recourse to anything other than the natural light of reason. Clearness and distinctness are not the same: I perceive an idea clearly when I comprehend it intellectually without any assistance from the senses or from agencies outside my own innate reasoning powers. But such an idea may be mixed with less clear, more confused intellectual notions, in which case it is not distinct. It is only when I consider it in its-distinct form that I am in a position to judge of its truth or falsehood.

Having established his own existence and introduced the concept of a ‘natural light’ of reason whereby to advance from this premise to whatever conclusions may spring from it, Descartes went on to reflect on his own nature. It is clear, he argued, that I am a thing which thinks. Moreover, since I cannot conceive myself except as thinking, it is of my essence to think. (‘Think’—
cogitare
—was a word of wide application for Descartes, and covered all conscious manifestations of the mental life.) Now, however hard I try, I can find no other property besides thought which belongs to my essence. For example, although it seems to me that I have a body which I can move at will, I can readily conceive of myself as existing without this body. Hence it is not an essential property of me that I have a body. I could conceivably (although it is a matter of faith that I will in fact) exist after the body’s demise. And in so existing I shall continue to exist as a thinking thing.

That argument, which contains Descartes’ grounds for asserting at least the possibility of immortality, can be criticised on many grounds. (In particular there is a confusion in the idea that since I cannot conceive myself as not thinking it is therefore of my essence to think.) However, it formed the basis of a Cartesian thesis of great importance, a thesis which dominated philosophy for centuries, and which Descartes expressed by saying that there is a ‘real distinction’ between body and soul. Associated with this thesis is a view to which we shall shortly return and which I shall label, in deference to recent discussions, the ‘Cartesian theory of mind’.

Having established his own existence and nature, Descartes now seeks to overcome the corrosive doubt which had earlier beset him, so as to be able to set up a sure foundation for his knowledge of the external world. So far, it will be noted, Descartes’ conclusions have concerned only himself and the contents of his own consciousness. And his very method of doubt has forced him into the confines of what I shall call ‘the first-person case’, beyond which he has so far found no argument that will open the passage. However, it is clearly important that he should find that argument, for his enterprise requires it. He wishes to arrive at a view of the world which is, in a quite specific sense, objective. That is to say, he wishes to show that a world exists independently of his thoughts and perceptions, a world that might at any moment be other than it appears to him to be, a world of which he is but one finite, fallible part, and the true nature of which he may discover only by laborious enquiry. The peculiarity of the first person is, roughly speaking, that from the first-person point of view the distinction between being and seeming does not arise. My conscious mental states are as they seem to me, and seem to me as they are: what else, after all, is meant by ‘consciousness’? Knowledge of the first person signally fails to reach out beyond subjectivity to the concept of an objective independent order. For the concept of such an order is the concept of a potential divergence between being and seeming. This divergence will not be made available to Descartes simply by reflecting on his own present state of mind.

Descartes therefore needed to establish the existence of at least one being independent of himself and in relation to which he could situate himself as part of an objective world. It is characteristic of Descartes’ time, and of the element in his philosophical method that was later to be designated as ‘rationalism’, that he should choose at this point to establish the existence of God. The methodological importance of this choice was, as we shall see, enormous.

Descartes had two arguments for the existence of God, versions of the ‘cosmological’ and the ‘ontological’ arguments respectively. Both of them illustrate the extent to which his thought, for all its radical departures from scholastic tradition, remained true to the medieval conceptions which his philosophical education had bequeathed to him. The two arguments are as follows. First: I am an imperfect being (as is proved by the fact that I can doubt and therefore do not have perfect knowledge). But I have the idea of a most perfect being (of God), and whence came this idea? It could not be of my own devising, since it is manifest to the natural light of reason that there must be ‘as much reality (perfection) in the cause as in the effect’. Applying this principle to ideas, it manifest that there must be as much ‘formal reality’ in the cause of an idea as there is ‘objective reality’ in the idea itself. ‘Formal’ means actual, and ‘objective’ represented. The more reality represented by an idea, the greater the reality that produced it. My idea of God represents the highest degree of reality; its cause therefore must be real in the highest degree; in short, it must be God himself.

The argument depends upon the premise, said to be manifest to the natural light, but in fact hardly intelligible, that there is at least as much reality in the total cause as in the effect. Included in this premise is precisely the set of suppositions required by the second argument— namely, that reality admits of degrees and is therefore a predicate or property of things, and that reality (or existence) is a positive property or ‘perfection’. If we allow these suppositions, then Descartes’ version of the ontological argument follows at once. I have an idea of a most perfect being; I clearly and distinctly perceive that such a being must contain all perfections, and therefore reality in every degree. Hence this idea contains existence, which means that God’s essence contains his existence. (Of no other thing, Descartes adds, can this be said.)