A Short History of Modern Philosophy: From Descartes to Wittgenstein, Second Edition (7 page)

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.

There are two further respects in which the Port-Royal logic deserves recognition. First, because of its quasi-mathematical development of part of the medieval logic. This development must have seemed natural to any follower of Descartes, but it contained the first premonition of modern formal logic. Secondly, because of its distinction, again novel at the time but now considered fundamental to logic, between the ‘comprehension’ and ‘extension’ of a general term. The word ‘comprehension’ denotes that which is understood in understanding a term—in other words, the idea that the term expresses. The extension of a term, on the other hand, is the set of things to which it is applied. (Thus the comprehension of the term ‘man’ is the idea of manhood, its extension is the class of men.) Following the nineteenth-century Scottish philosopher Sir William Hamilton, the distinction is now often expressed as that between the intension and the extension of a term. It was important to Arnauld and Nicole, since they wished to isolate the former (the realm of ‘ideas’) as giving the true subject matter of logic; it is important in modern thought for the opposite reason, because logicians have come increasingly to realise that logic is the science not of the intension, but of the extension of terms (see chapter 17).

The Port-Royal school projected a manual on mathematics, and, as a preface to this, Blaise Pascal (1623-1662) wrote his
De l’esprit géometrique,
an investigation into the philosophy of mathematics designed to display not just the nature of the ‘geometrical’ method, but also its limits. Pascal, like Descartes, was a great mathematician and a deeply religious man. But his faith, which he acquired by conversion, took the passionate form characteristic of Jansenism, according to which the claims of reason could never suffice as foundations for so great a thing as religious doctrine. Pascal argued that the indefinability of terms and the need for axioms in the ‘geometrical method’ showed not the absolute validity of the ‘clear and distinct idea’, but rather the imperfection of finite minds, which must always rest content with indefinables. Our reason may give us some guarantee of the methods of the geometer, but it could never provide the same guarantee for his axioms.

In the famous
Pensées
(published posthumously) Pascal takes further his strictures on the use of reason, arguing that, since God is hidden from mortal view, it is futile to attempt to discover his essence through rational enquiry. ‘We know truth not only by reason but more by the heart.’ And it is from the heart that we sense the meaning of life and its divine eschatology. Pascal stopped short of total scepticism, believing it to be self-defeating, and qualified his strictures against rational theology with a curious argument for the existence of God: ‘Pascal’s wager’. The argument goes roughly as follows: ‘If God exists He will reward belief in Him: while if He does not exist, such belief leads to no harm. Hence the best bet is to believe in Him.’ The argument reflects Pascal’s concern with the concept of probability; it is interesting because it offers practical reasons (rather than theoretical reasons) for an article of faith, so connecting the logic of religious belief not with that of science but with that of practice. This singularly modern idea—which resurges periodically in later philosophy, for example in Kant’s conception of the ‘ideas’ of reason, in Kierkegaard’s notion of the ‘leap’ of faith, in the neo-Marxist theory of
praxis
and in the existentialist concept of commitment—possesses less philosophical merit than rhetorical impact.

For while it is indeed a striking suggestion that religious belief may be constituted by a form of voluntary activity, and so be inaccessible to metaphysical doubt, it seems hard to reconcile with the obvious fact that the question of the existence of God is a question about what is true, and not a question that could be resolved by mesmerising ourselves into a state of unfounded belief in Him.

Perhaps the greatest of the many philosophers who could reasonably be called Cartesian was Nicolas Malebranche (1638-1715), a priest of the Oratory who engaged in a vivid and at times bitter controversy with Arnauld over matters of theology and metaphysics. Like Pascal, Malebranche was distinguished by his literary gifts and produced—in his
Dialogues on Metaphysics (Entretiens sur la métaphysique et sur la religion,
1688)—some of the finest philosophical prose since Plato. But he did not share Pascal’s distrust of metaphysics and conceded to mysticism only a narrow region of carefully circumscribed darkness. Malebranche had thoroughly absorbed the principles and proofs of the Cartesian philosophy, but, like many who were convinced that Descartes’ method was both valid and comprehensive, he remained unsatisfied with the Cartesian picture of the relation between body and soul.

Descartes’ views of causation are such that there is a
prima facie
contradiction between the thesis that body and soul are (or exemplify) separate substances, and the thesis that there is also interaction between them. Malebranche did not seek to question the Cartesian idea of substance, although his writings are remarkable for containing an extended metaphysics from which that idea could be eliminated without detriment to the system’s integrity. Instead, he questioned the theory of causation implicit in Descartes: the theory that the states of a substance must be explained in terms of its essential nature. It seemed to Malebranche that such a theory could explain neither our ability to perceive the material world, nor our ability to act on it. Furthermore (and in this he showed how much he had let the Cartesian conception of material substance fall into the background of his philosophy, replacing it with the more modern idea of the material object), he even regarded it as incompatible with the view that there is causal action between separate bodies, since it seemed to imply that each body, being complete in itself, had nothing to gain from or to impart to its surroundings. Rejecting the view that bodies have an intrinsic ‘power’ to affect us and each other as a mere superstition, Malebranche adopted the theory, already proposed by the Cartesians du Cordemoy (c. 16051684) and Arnold Geulincx (1624-1669), of ‘occasionalism’, which he defended with great vigour. This theory—perhaps the first developed account of the concept of causation in modern philosophy—argues that, since the laws of the universe have their origin in God, it is God who produces the events that conform to them. No event produces another of its own nature. Rather, when one thing occurs, then this is the occasion for God’s production of that thing which we know as its ‘effect’. In this view, there is no special difficulty posed by the relation between mind and body, since to speak of interaction between them can only be a manner of speaking: just as it is only a manner of speaking to refer to interaction between anything.

There is much more to Malebranche’s metaphysics than this theory (often wrongly thought to be, not a general philosophy of causation, but rather an
ad hoc
apologetic whereby to reconcile the Cartesian theory of mind with the obvious). In particular Malebranche upheld and developed the Cartesian theory of continuous creation; he supported the view that science must be rooted in
a priori
metaphysical principles; and he reaffirmed the distinction between the rationally conceivable essence and the empirically perceivable properties of things. But his influence in these matters was less great than it might have been. The Cartesian philosophy was already being eclipsed by the more systematic work of Spinoza and Leibniz, and by the powerful attack on rationalism initiated by Hobbes and given magisterial form in Locke’s
Essay on the Human Understanding.

It is impossible to leave the subject of the Cartesian revolution without taking a brief forward glance into that intellectual movement known to the historian of ideas as the ‘Enlightenment’, and known to philosophers either as the eighteenth century, or as nothing at all. By the end of the seventeenth century, scientific knowledge, and the Cartesian clarity of expression, had become universal properties of the educated class; and a new literature began to arise, encyclopaedic in its aims, antiauthoritarian in its preconceptions and outspoken in its style (see especially Pierre Bayle (1647-1706):
Dictionnaire historique et critique,
1696). Culminating in the writings of Voltaire, Diderot and d’Alembert, this movement has gained international status in the eyes of the intellectual historian. But it remains decidedly French in its tone and manners. Clear, elegant, haughty and ironical, the
‘philosophes’,
as they came to be known, stand at the end of a century in which intellectual, political and moral revolutions had upset the authority of Church and State, and humbled in their eyes all mortals whose pretensions to eminence could be backed neither by reason nor by experiment. Most of the
philosophes
had their intellectual roots in Cartesian scepticism; but by now this scepticism, separated from the intellectual accomplishment of the metaphysics which stemmed from it, had become a literary device, a means to sustain a detached attitude of rational unbelief, while treating of matters that could allow neither systematic development nor the easy extraction of a moral.