I answer that, {synesis} (judging well according to common law) signifies a right judgment, not indeed about speculative matters, but about particular practical matters, about which also is prudence. Hence in Greek some, in respect of {synesis} (judging well according to common law) are said to be {synetoi}, i.e. "persons of sense," or {eusynetoi}, i.e. "men of good sense," just as on the other hand, those who lack this virtue are called {asynetoi}, i.e. "senseless."
Now, different acts which cannot be ascribed to the same cause, must correspond to different virtues. And it is evident that goodness of counsel and goodness of judgment are not reducible to the same cause, for many can take good counsel, without having good sense so as to judge well. Even so, in speculative matters some are good at research, through their reason being quick at arguing from one thing to another (which seems to be due to a disposition of their power of imagination, which has a facility in forming phantasms), and yet such persons sometimes lack good judgment (and this is due to a defect in the intellect arising chiefly from a defective disposition of the common sense which fails to judge aright). Hence there is need, besides {euboulia} (deliberating well), for another virtue, which judges well, and this is called {synesis} (judging well according to common law).