 After discussing the nine objections mentioned above, Turing goes on to say that he has “no very convincing arguments of a positive nature to support my views. If I had I should not have taken such pains to point out the fallacies in contrary views.” (454) Perhaps Turing sells himself a little short in this self-assessment. First of all—as his brief discussion of solipsism makes clear—it is worth asking what grounds we have for attributing intelligence (thought, mind) to other people. If it is plausible to suppose that we base our attributions on behavioral tests or behavioral criteria, then his claim about the appropriate test to apply in the case of machines seems apt, and his conjecture that digital computing machines might pass the test seems like a reasonable—though controversial—empirical conjecture. Second, subsequent developments in the philosophy of mind—and, in particular, the fashioning of functionalist theories of the mind—have provided a more secure theoretical environment in which to place speculations about the possibility of thinking machines. If mental states are functional states—and if mental states are capable of realisation in vastly different kinds of materials—then there is some reason to think that it is an empirical question whether minds can be realised in digital computing machines. Of course, this kind of suggestion is open to challenge; we shall consider some important philosophical objections in the later parts of this review.