A Short History of Modern Philosophy: From Descartes to Wittgenstein, Second Edition by Unknown Author Page B

thinking (an idea), we situate it in the total system of ideas (which is God, conceived under the attribute of thought). No explanation of an idea can be formulated, except in terms of other ideas. Similarly, when we describe a mode of extension, we situate it in the system of physical things, and explain it accordingly, through the attribute of extension. Mind and body are one thing; but they are conceptualised under rival and incommensurable systems. Hence, while we can assert in the abstract that they are identical, we can never explain a physical process in terms of a mental one, or a mental process in terms of a physical. This combination of doctrines has proved immensely puzzling to Spinoza’s commentators. On the one hand, he is a monist, believing that there is only one ultimate reality, of which everything is a mode; on the other hand, he admits a kind of dualism into his system, reaffirming the separateness of mind and body in the very act of denying it.
    Perhaps the best way to grasp what Spinoza is saying is through a somewhat distant analogy. When I look at a picture I see physical objects: patches of pigment smeared on a canvas. And I can describe these objects so thoroughly as to account for the entire picture. In doing so, I do not mention the other thing that I see: a stag hunt passing before a country house. This too I could describe so thoroughly as to give a complete account of the picture. But the two accounts are incommensurable: I cannot cross from one to the other in midstream, so to speak. I cannot describe the lead hound as frantically pursuing a patch of ochre, or the area of chrome yellow fused with oxydised linseed oil as resting on the huntsman’s knee. In some such way, Spinoza is saying, the complete description of the body describes the very same thing as the complete description of the mind; but to explain mental states in terms of physical causes is to cross in midstream to another and incommensurate language.
    Persons and things
    What, then, are we? To say that we are modes of the divine substance is not to say enough, for, as Spinoza realised, this does not yet grant to us our individuality. In particular, it does not settle the important question of how we can come to consider ourselves as things, even though, in the nature of the case, we cannot be substances. Thus Spinoza, having argued that there can be only one substance, attempted to reconcile this doctrine with the view that there is a potentially indefinite number of things. He did this by reversing Descartes’ argument about the wax.
    The wax, it will be remembered, seemed not to possess any essential unity or identity beyond that of the stuff out of which it was composed. It could be broken up, melted, transformed in respect of every one of its properties except those which pertained to matter as such. Its individuality counted for nothing in comparison with its constitution. By contrast, Spinoza observes, there are certain modifications of fundamental substance which have a kind of innate resistance to changes of the kind undergone by Descartes’ lump of wax. Things resist damage, fracture and so on, or perhaps, if injured, they restore themselves out of their own inherent principle of existence. They endeavour, as Spinoza puts it, to persist in their own being. This endeavour (conatus) constitutes their essence, in so far as it makes sense to attribute essence to something that has neither the completeness nor the self-sufficiency of a genuine substance.
    The obvious examples of these partial substances or individual things are organisms; and in describing their identity in terms of a conatus Spinoza was in effect reviving a concept from Aristotelian biology. Organisms seem to have more conatus than inanimate things: they avoid injury, resist it, restore themselves when it is inflicted. This is why we are ready to attribute to them an individuality that we are not always willing to attribute to inanimate objects. We speak of