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John Locke distinguished between the real and nominal essence of substances such as water. The real essence of a substance is its hidden ‘inner constitution’: we now know that the real essence of water is H2O. The nominal essence of a substance is its observable properties: the nominal essence of water is the way it looks, tastes, feels, etc.
Something is an instance of a substance just if it has the essence of that substance. Locke held that something is water just if it has the nominal essence of water, just if it tastes, feels and looks like water. If something has the nominal essence of water, but is not H2O, it is nevertheless water. And if something is H2O, but does not have the nominal essence of water, it is not water. Part of his reason for holding this was his view that we cannot know the real essence of a substance—its hidden ‘inner constitution’.
The view that we cannot know the real essences of substances has been overturned by the progress of science. After all, we now know that the real essence of water is H2O. Contemporary philosophers hold that something is water just if it has the real essence of water, just if it is H2O. If something has the real essence of water, but does not look, taste, or feel like water, it is nevertheless water. And if something looks, tastes, and feels like water, but is not H2O, then it is not water. AJ
See also essentialism.Further reading J.L. Mackie, Problems from Locke; , S. Kripke, Naming and Necessity. |
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