 This definition is essentially circular; it is not reducible to one in normal form. Still, intuitively, it provides substantial guidance on the use of \(G\). The definition dictates, for instance, that Socrates falls under \(G\), and that nothing apart from the three ancient philosophers mentioned does so. The definition leaves unsettled the status of only two objects, namely, Plato and Aristotle. If we suppose that Plato falls under \(G\), the definition yields that Plato does fall under \(G\) (since Plato satisfies the definiens), thus confirming our supposition. The same thing happens if we suppose the opposite, namely, that Plato does not fall under \(G\); again our supposition is confirmed. With Aristotle, any attempt to decide whether he falls under \(G\) lands us in an even more precarious situation: if we suppose that Aristotle falls under \(G\), we are led to conclude by the definition that he does not fall under \(G\) (since he does not satisfy the definiens); and, conversely, if we suppose that he does not fall under \(G\), we are led to conclude that he does. But even on Plato and Aristotle, the behavior of \(G\) is not unfamiliar: \(G\) is behaving here in the way the concept of truth behaves on the Truth Teller (“What I am now saying is true”) and the Liar (“What I am now saying is not true”). More generally, there is a strong parallel between the behavior of the concept of truth and that of concepts defined by circular definitions. Both are typically well defined on a range of cases, and both display a variety of unusual logical behavior on the other cases. Indeed, all the different kinds of perplexing logical behavior found with the concept of truth are found also in concepts defined by circular definitions. This strong parallelism suggests that since truth is manifestly a legitimate concept, so also are concepts defined by circular definitions such as (18). The paradoxes, according to this viewpoint, cast no doubt on the legitimacy of the concept of truth. They show only that the logic and semantics of circular concepts is different from that of non-circular ones. This viewpoint is developed in the revision theory of definitions.