And so of all other things;—justice is useful when they are useless, and useless when they are useful?

That is the inference.

[E]Then justice is not good for much. But let us consider this further point: Is not he who can best strike a blow in a boxing match or in any kind of fighting best able to ward off a blow?

Certainly.

And he who is most skilful in preventing or escaping[2] from a disease is best able to create one?

[2] Reading φυλάξασθαι καὶ λαθεῖν, οὗτος, κτλ.

True.

A new point of view: Is not he who is best able to do good best able to do evil? And he is the best guard of a camp who is best able to [334]steal a march upon the enemy?

Certainly.

Then he who is a good keeper of anything is also a good thief?