<p>What is an argument? This foundational question in argumentation research cannot be answered univocally, because ‘argument’ is ambiguous. This paper has two goals. The first is to draw attention to a neglected distinction between two ordinary ‘logical’ senses of the term: an ‘objective’ and a ‘subjective’ one. The second is to define these senses. In the objective sense, an argument for (or against) a certain proposition is a reason for (or against) believing that proposition. In the subjective sense, it is a consideration intended to provide such a reason. After defining these two senses, the paper defends these definitions against several objections. In this connection, I argue, among other things, that conclusions are not internal parts of arguments; that premises and conclusions are not ‘speech acts’; that the subjective sense of ‘argument’ is robust against the charge of relativism; and that considerations can deserve the name ‘argument’ even if they do not provide actual support.</p>