The problem of individuation

Suppose we have before us two red, round spots named Socrates and Plato. Socrates and Plato are exactly alike in all their qualities (i.e. properties). Since they have the same size, shape, color and so on, Socrates and Plato are a cause of what is called quality agreement.

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Given that two things have exactly the same properties, how is that the two are not the same thing? What differentiates them and makes them two individuals? Consider the two spots Plato and Socrates at the begining of this chapter. They share all their properties in common. If properties are universals (both spots have the very same properties), what then is it that makes them two spots instead of just one? One may be tempted to say that the spots are different because of their different spatial locations on a sheet of paper. But clearly, this will not do. Why? Because two spots cannot be at different locations if, metaphysically speaking, they are not already different spots. Difference of spatial locations presupposes difference and individuation and thus cannot constitute individuation.

The same problem of individuation arises with individual substances. If Smith and Jones have the very same human nature, then how are they different? What makes them two humans instead of one?

Philosophical Foundations for a Christian Worldview

J.P. Moreland & William Lane Craig

InterVarsity Press, 2003

Pages 204, 219