When you want a deposit to be kept safely.
You mean when money is not wanted, but allowed to lie?
Precisely.
That is to say, justice is useful when money is useless?
That is the inference.
And when you want to keep a pruning-hook safe, then justice is useful to the individual and to the state; but when you want to use it, then the art of the vine-dresser?
Clearly.
And when you want to keep a shield or a lyre, and not to use them, you would say that justice is useful; but when you want to use them, then the art of the soldier or of the musician?
Certainly.
And so of all the other things;—justice is useful when they are useless, and useless when they are useful?