It has been already pointed out that Descartes intended to replace Aristotelian philosophy. This intention necessarily shows itself in his treatment of the substance and accident. One of the main differences consist in Descart’s denial of the reality of accidents. “Secondly it is completely contradictory that there should be any real accidents, since whatever is real can naturally exist separately from any other subject; yet anything that can exist separately in this way is a substance and not an accident.”1
Although particular accidents and relations were a matter of dispute through the whole history of perennial philosophy, their objectivity was not doubted, although they were understood to exist by the way of participation. Basis for this was Aristotle’s distinction between the substance itself and the properties of the substance. Accident is one of the five universal predicables which qualify any substance. Descartes would not be at odds with this, for he accepts the list of five universal notions. “Hence five universals are commonly listed: genus, species, differentia, property and accident.”2
However, for Descartes accidents are modes of things. Thus he defines in the Principles of Philosophy that all the numbers and universals are mere modes of thinking.3 Further, Descartes makes a distinction in between the mode and attribute. An attribute is something which really belongs to the nature of the thing. “But considered in itself, the extension itself – the subject of these modes – is not a mode of the corporeal substance, but an attribute which constitutes its natural essence.”4 The mode on the other hand is not part of the substance for the substance can be understood apart form it. Mode is defined similarly as the accident in perennial philosophy. “As I explained above, the nature of a mode is such that it cannot be understood at all unless the concept of the thing of which it is a mode is implied in its own concept”5 Modes thus become unintelligible apart from the concept of the substance in which they inhere and they also are less permanent and real then attributes and substances. This is simply because there are two types of created substances, namely the thinking ones and the extended ones. There is always only one essential attribute and finally modes are simply modes of this attribute, they are ways of its existence. “A substance may indeed be known through any attribute at all; but each substance ha only one principal property which constitutes its nature and essence, and to which all other properties are referred.”6
Finally, Descartes undertakes to demolish the theory of real accidents. He presupposes that the theory of real accidents was invented because people used to think that they are affected by the real accidents. Now since to him the only think which affects us is the mode of surface, there is no need for real accidents.
In order to demolish the doctrine of the reality of accidents, I do not think we need to look for any arguments beyond those I have already deployed. First, since all sense-perception occurs through contact, only the surface of a body can be the object of sense-perception; yet if there were real accidents, they would have to be something different from the surface, which is nothing but a mode; and hence, if there are any real accidents they cannot be perceived by the senses. But surely the only reason why people have thought that accidents exist is that they have supposed that they are perceived by the senses.7
However, this transformation is a result of Cartesian understanding of sense perception. Firstly, Descartes in some way agrees with Aristotle that the core of all sense perception is physical contact, however he reduces the object of this contact to surface only. “For contact with an object takes place only at the surface, and nothing can have an effect on any of our senses except through contact, as not just I bu all philosophers, including even Aristotle, maintain.”8 Secondly, since Descartes is a dualist and the soul is joined with the body only through the brain, the communication in between the moment of contact and brain is explained in a completely material way and the need and reality of the intentional forms becomes therefor obsolete for Descartes.9 Therefore, all the sensing happens through the senses being affected by the other material thing itself. Material things simply affect the body and its nerve system in a certain way and then by means of this nerve system the brain is affected and finally the soul through the brain. “And the various different states of mind or thoughts, which are the immediate result of these movements are called sensory perceptions, or in ordinary speech, sensations.”10 Now, the nerves transmit only local motion and therefore can be affected only in such a way. Thus for Descartes it is only shape, size and motion which really affects the nerves, whereas all other sensations are dispositions of shape, size and motion which affect the body in a particular way. “Now we understand very well how the different size, shape and motion of the particles of one body, can produce various local motions in another body.”11 Therefore certain modes of material things are result of the ways in which nerves communicate them to mind and secondly are apart form the material substance unintelligible. This shall be later considered with respect to the mystery of the Eucharist and Cartesian treatment of it.
1AT, 7 : 434.
2AT, VIII A: 28.
3Comp.: AT, VIII A: 27.
4AT VIII B: 348 -349.
5AT VII B: 355.
6AT VIII A: 25.
7AT VII: 434.
8AT VII: 249.
9“For example when I see a stick, it should not be supposed that certain ‘intentional forms’ fly off the stick toward the eye, but simply that rays of light are reflected off the stick and set up certain movements in the optic nerve and, via the optic nerve, in the brain, as I have explained at some length in the Optics.” AT VII : 436.
10AT VII: 316.
11AT VIII A: 322. In the end of 198th principle of the fourth book of The principles of Philosophy Descartes finally concludes: “In view of all this we have every reason to conclude that the properties in external objects to which we apply the terms light, colour, smell, taste, sound, heat and cold – as well as other tacile qualities and even what are called ‘substantial forms’ – are, so far as we can see, simply various dispositions in those objects which make them able to set up various kinds of motions in our nerves< which are required to produce all the various sensations in our soul>.” AT VIII A: 322-323.