Acceptance By Performance or By a Promise

Suppose Alice's offer invites acceptance either by walking across the bridge, or by promising to do so. Imagine she says, "I offer you $500 to walk across the Michigan Avenue bridge. You may accept either by walking across the bridge or by promising to do so."

The rule is that, if the offer invites acceptance either by a performance or by a promise, then beginning performance is acceptance by performance of the offer, where the beginning of the performance is a promise to complete the performance. See Restatement (Second) Contracts § 62.

Thus, Bob

does not accept Alice's offer until he walks all the way across the bridge because walking all the way is the performance Alice requested.

accepts Alice's offer when he begins to walk across the bridge even though walking all the way is the performance Alice requested.