  Socrates’ basic objection to this theory is that it still gives no proper explanation of how this logical construction takes place. Without such an explanation, there is no good reason to treat the complexes that are thus logically constructed as anything other than simples in their own right. We need to know how it can be that, merely by conjoining perceptions in the right way, we manage to achieve a degree of semantic structure that (for instance) makes it possible to refer to things in the world, such as Theaetetus. But this is not explained simply by listing all the simple perceptions that are so conjoined. Nor—and this is where we reach the third proposal of 208b11–210a9—is it explained by fixing on any of those perceptions in particular, and taking it to be the special mark of Theaetetus whereby reference to Theaetetus is fixed.