All three statements are correct. Consideration is indeed the recompense given by the party contracting with the other (it's the price paid for the promise). Past consideration is generally no consideration because it doesn't involve the element of bargain - if the act was done before the agreement, it cannot serve as consideration. And consideration must have some value in the eyes of the law, though it need not be adequate. The doctrine of consideration requires a bargained-for exchange between parties.