What serves as a rejection of an offer?

A counteroffer serves as a rejection of an initial offer because it effectively alters the terms of the original proposal. When the offeree presents a counteroffer, they are not simply accepting the original terms; instead, they are introducing new terms that must be agreed upon for a contract to be formed. This act implies that the offeree is not willing to accept the original offer as it stands, thus rejecting it.

In contrast, a contingency is a condition that must be met for the contract to be enforceable, but it does not reject the offer; rather, it seeks to modify the acceptance of the offer based on certain events. An amendment refers to a change made to an existing agreement and does not reject an offer but rather alters its terms once both parties agree. An addendum is an additional document that adds conditions or terms to an existing contract without rejecting any previous offers. Thus, a counteroffer distinctly stands out as the action that explicitly rejects the original offer.