Nemo extensio in longum, latum et profundum, substantiae corporea naturam constituit (extension in length, breadth, and thickness constitutes the nature of corporeal substance). (Principles of Philosophy, Book I).This is Descartes' definition of matter. He goes on to elucidate it in this way: 'Everything else that can be ascribed to body presupposes extension.' The other qualities of matter, then, are less important and he tells us 'though substance is indeed known by some attribute, yet for each substance there is pre-eminently one property which constitutes its nature and essence and to which all the rest are referred'. The pre-eminent property of corporeal substance which constitutes its essence and nature is extension. The essence of matter then is extension, according to Descartes. As he puts it in his physical treatise 'Le Monde' , referring to matter he tells us 'I conceive its extension, or the property it has of occupying space, not at all as an accident, but as its true form and essence.' Extension is the essence of matter then. Whatever has spatial extension is matter and matter, by definition, is that which has spatial extension. Spatial extension, then, constitutes matter. What is spatial extension? It is length, breadth and thickness, the three straight lines that constitute Euclidean space. So that which has length, breadth and thickness is matter and all matter, on this definition, has length, breadth and thickness.
I observed that nothing at all belonged to the nature of essence of body except that it was a thing with length and breadth and depth, admitting of various shapes and various motions. I found also that its shapes and motions were only modes, which no power could make to exist apart from it; and on the other hand that colours, odours, savours and the rest of such things, were merely sensations existing in my thought and differing no less from bodies than pain differs from the shape and motion of the instrument which inflicts it.He then goes on to explain that he considered other properties of bodies to be modes of motion and so on. Gravity, for example, was for him reducible to motion and he tried to explain the various phenomena in terms of vortices of particles of varying sizes and velocities. He accepted the logical consequences of his identification of spatial extension and matter and denied the possibility of a vacuum in nature notwithstanding the work of his contemporaries Pascal and Torricelli. But I believe the idea of nature as a plenum has come back into fashion. (Newtonian space was distinct from matter and was envisaged as an empty container but the Theory of Relativity has united space and matter in Cartesian fashion.).
The birth of modern science was preceded and accompanied by a development of philosophical thought which led to an extreme formulation of the spirit/matter dualism. This formulation appeared in the seventeenth century in the philosophy of Rene Descartes who based his view of nature on a fundamental division into two separate and independent realms; that of mind (res cogitans), and that of matter (res extensa).There are assumptions here of course. Perhaps it is just not possible to talk about 'matter' without also talking about 'mind'. It is after all some mind that is doing the talking. Perhaps it is also not possible to talk about 'mind' without giving it a local habitation and a name - that is by mentioning matter. It was Descartes after all who first infected us with doubt so that he allowed, for example, only a doubtful inferential knowledge the existence of our own bodies. In the philosophy of Descartes the very existence of matter is called into question. According to Descartes, the existence of matter including our own bodies is not self-evident. He sees nothing incoherent in doubting the existence of one's own body. (But one could not doubt that 'mind' or thinking thing existed.) To talk, then, of matter in isolation from mind is contrary to the whole spirit of his philosophy which is rooted in epistemology. But putting aside our Cartesian doubts for the moment, it is interesting to see how Descartes' treatment of matter was received in the nervous climate of the Counter-Reformation. Descartes' Meditations appeared in 1641. In 1663, thirteen years after his death it was put on the Index of prohibited books by Rome. True the ecclesiastical authorities did mollify their condemnation somewhat by appending the 'donec corrigantur' (Until Corrected), but as the dissident theologian Hans Kung tells us 'this was asking a lot from a dead man', and Copleston tells us that Descartes was still on the index at the time of writing his history of philosophy some three hundred years later. Now Descartes had tried to get his last major work, The Principles of Philosophy, adopted as a textbook in Colleges and seminaries. Why then was Descartes, a man who always kept a nervous eye on the clergy, put on the Index? Copleston, the Jesuit, informs us, that it was because Descartes' doctrine of matter and substance was incompatible with the dogma of transubstantiation which was proclaimed at the Council of Trent some time before Descartes' birth. The Church, in the period from the Council of Trent until the recent Vatican II, some four hundred years, had relied heavily on the Aristotelian/scholastic doctrine of substance and accidents or matter and form in its formulation of the dogma of transubstantiation. Descartes who was educated at school at the Jesuit College of La Fleche was brought up on the Aristotelian/Thomistic doctrine of matter. He must have been aware when he rejected this scholastic doctrine of matter and substance that he was living dangerously. If he had any illusions the Jansenist theologian, Arnauld, was soon to disillusion him. Arnauld pointed out to Descartes that his definition of matter was theologically unacceptable. I quote Arnauld:
But the chief ground of offence to theologians that I anticipate is that, according to M. Descartes' doctrines, the teachings of the Church relative to the sacred mysteries of the Eucharist cannot remain unaffected and intact.It is worth considering Arnauld's letter in some detail. We have seen that Descartes identified material substance and extension, but Arnauld refers to extension as one of the accidents. This was the traditional scholastic view. Again Arnauld tells us, 'M. Descartes recognizes no sense qualities'. These were what we would call the secondary qualities and as we have seen Descartes describes them as being in my thought'. Arnauld goes on to say that Descartes, 'acknowledges only a formal distinction between these affections and substance'. I think Arnauld here actually understates the charge against Descartes. His definition gives only a token recognition of substance. It is only a manner of speaking. 'Substance' disappears and with it the whole substance/accidents distinction. Of course Descartes replied to this, but he seems to me to concede the case when he writes
For it is an article of our faith that the substance of the bread passes out of the bread of the Eucharist, and that only its accidents remain. Now these are extension, figure, colour, odour, savour and the other sensible qualities.
But M. Descartes recognizes no sense-qualities, but only certain motions of the minute bodies that surround us, by means of which we perceive the different impressions to which we afterwards give the names of colour, savour, and odour. Hence, there remain figure, extension and mobility. But M. Descartes denies that those powers can be comprehended apart from the substance in which they inhere and that hence they cannot exist apart from it; and this is repeated in the reply to his critic.
Likewise he acknowledges only a formal distinction between these affections and substance, but a formal difference seems not to allow things so distinguished to be sundered from each other even by the Divine power.
I avow that I venture to hope that some day will come when the doctrine that postulates the existence of real accidents will be banished by theologians as being foreign to rational thought, incomprehensible, and causing uncertainty in the faith; and mine will be accepted in its place as being certain and indubitable.Descartes is here opposing the idea that there is even a conceptual possibility that substance and accidents could be separated and that consequently that 'real accidents' or independent accidents could exist. As we have seen Descartes defines substances in terms of their dominant accident or quality so that minds become 'thinking things' and matter extended things'.
The 'Cartesian' division allowed scientists to treat matter as dead and completely separate from themselves, and to see the material world as a multitude of different objects assembled into a huge machine. Such a mechanistic world view was held by Isaac Newton who constructed his mechanics on its basis and made it the foundation of classical physics. From the second half of the seventeenth to the end of the nineteenth century, the mechanistic Newtonian model of the universe dominated all scientific thought.Cartesian matter then is 'dead and completely separate from ourselves'. How then can we know it? The British empiricists, followers of Descartes in many things, defined matter in terms of sense-data' - that is quasi-mental elements and so side-stepped the whole issue. In fact the problem for them was to avoid idealism. But Descartes here, in his treatment of matter, seems to be assuming that matter is generically different from mind and yet can be confidently defined in complete isolation from mind. This is an assumption totally contrary to the spirit of systematic doubt, of epistemology. The scholastics built bridges between body and mind, and mind and matter, and so the dualism or polarity of Cartesianism. But Descartes derides the Hylomorphic matter/form doctrine. About substantial form he has this to say:
No one can doubt this who knows that these philosophical entities, which are unknown outside the schools, never crossed the minds of the prophets and apostles who composed the sacred scriptures at the dictation of the Holy Ghost. To prevent any ambiguity of expression, it must be observed that when we deny substantial forms, we mean by the expression a certain substance joined to matter, making up with it a merely corporeal whole, and which, no less than matter and even more than matter - since it is called an actuality and matter only a potentiality - is a true substance, or self-subsistent thing. Such a substance, or substantial form, present in purely corporeal things but distinct from matter, is nowhere, we think, mentioned in Holy Writ....And again in another letter:
They were introduced by philosophers solely to account for the proper actions of natural things, of which they were supposed to be the principles and bases, as was said in an earlier thesis. But no natural action can be explained by these substantial forms, since their defenders admit that they are occult and that they do not understand them themselves. If they say that some action proceeds from a substantial form it is as if they said that it proceeds from something they do not understand; which explains nothing.'They explain nothing' - this is the essence of Descartes case against substantial forms. They are non-observables. All the quiddities, essences, substantial forms, entelechies, perfective principles and the rest of scholastic matter were banished by Descartes, the great simplifier. Hundreds of years of intense debate were wiped out by Descartes. Scholasticism had proved to be sterile and a fresh start was required. His definition ignores substantial forms: 'extension in length, breadth, and thickness constitutes the nature of corporeal substance'. The definition is phenomenal:- matter has been denuded of its 'within' as Teilhard de Chardin would call it. It is a geometer' s definition of matter, without colour, taste or warmth and it is pragmatic and operational and free from any distracting metaphysical undertones. It is simple. It is intelligible. Matter is described in Euclidean terms. It includes both animate and inanimate nature as Descartes was an anti-vitalist who believed nature could be understood in mechanistic terms.
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