For Aristotle, it is that they can see the "truth in concrete things":
Hence, we must ask the spoudaios, who differs from other men in that he sees "truth in concrete things" (hekastois), for he is, as it were, their standard and measure (kanon kai metron) (NE 1113a34)–a principle of method to which our "empirical" social scientists should pay heed.Neither Aristotle, nor Voegelin, nor I, were / are against abstraction, which can be very useful. Doing something like a statistical study of economic conditions prior to revolutions might prove interesting. But knowledge of the abstract is inferior to and derivative of knowledge of the concrete.
The passages dealing with the spoudaios show very clearly that Aristotle cannot view what is right by nature as a natural law, a set of eternal, immutable propositions, because the truth of a concrete action cannot be determined by its subsumption under a general principle, but only by questioning the spoudaios.