Concurrent covenants are those which, by the terms of the contract, are each to be performed at the same time by each of the parties who are respectively bound to perform each.1 The practical effect of treating a covenant as concurrent with another, is manifest chiefly in the necessity of making tender or informal offer of performance by the one party in order to put the other in default; or, in other words, in the right of either party to enforce one of such covenants against the adversary party without himself tendering performance or offering it informally. These questions are considered subsequently.2