  The main idea about statements is simple: a statement has structure and its parts perform different functions. The name (grammatical subject) refers to something, and if it fails to pick out anything the statement does not come off (Sophist 262e). The verb (predicate) ascribes to that thing an action (or property). If someone asserts of a subject a predicate ascribing to it something that is (the case) about it (an action the thing is actually performing or an attribute it actually has), the statement is true; whereas if he asserts of it a predicate ascribing something that is not (the case) about it (something different from what is the case about it), then the statement is false (Sophist 263b). For instance, when the Stranger says of Theaetetus, who is currently sitting, “Theaetetus is sitting,” his statement is true because it asserts something that is the case about Theaetetus; but when he says of Theaetetus (still sitting), “Theaetetus is flying,” his statement is false, because “flying” specifies something different from what is the case about Theaetetus (namely, sitting).