 G. E. Moore drew attention to a point that might look (and has been held to be) problematic for the identity theory (Moore 1953: 308; Fine 1982: 46–7; Künne 2003: 9–10). The proposition that Socrates is wise exists in all possible worlds where Socrates and the property of wisdom exist, but in some of those worlds this proposition is true and in others it is false. The fact that Socrates is wise, by contrast, only exists in those worlds where the proposition both exists and is true. So it would seem that the proposition that Socrates is wise cannot be identical with the fact that Socrates is wise. They have different modal properties, and so by the principle of the indiscernibility of identicals they cannot be identical.