  Socrates offers two objections to this proposal. First, if knowledge of Theaetetus requires a mention of his sêmeion, so does true belief about Theaetetus. Second, to possess “an account of Theaetetus’ sêmeion” must mean either (a) having true belief about that sêmeion, or else (b) having knowledge of it. But it has already been pointed out that any true belief, if it is to qualify as being about Theaetetus at all, must already be true belief about his sêmeion. So interpretation (a) has the result that knowledge of Theaetetus = true belief about Theaetetus’ sêmeion + true belief about Theaetetus’ sêmeion. As for (b): if we want to know what knowledge is, it is no help to be told that knowledge of O = something else + knowledge of the sêmeion of O. We still need to know what knowledge of the sêmeion of O is. Nor will it help us to be launched on a vicious regress: as we will be if we are told that knowledge of the sêmeion of O = something else + knowledge of the sêmeion of the sêmeion of O.  