Again expediency is sometimes determined by the nature of things, sometimes by the circumstances of the time. Another common subject of controversy is whether a law can be enforced, while one must not shut one's eyes to the fact that exception is sometimes taken to laws in their entirety, but sometimes only in part, examples of both forms of criticism being found in famous speeches.

I am well aware, too, that there are laws which are not proposed with a view to perpetuity, but are concerned with temporary honours or commands, such as the lex Manilia The lex Manilia proposed to give Pompey the command against Mithridates. which is the subject of one of Cicero's speeches. This however is not the place for instructions on this topic, since they depend on the special circumstances of the matters under discussion, not on their general characteristics.