Let us suppose that a person P tries to communicate to another person Q a proposition and the standpoint that this proposition is tenable. Let us further suppose that P tries to express it by a sentence T0, and that Q reacts positively in such a way as to indicate «agreement» with P. This act of assenting may be performed by means of words such as «yes», «sure», «certainly », «agreed», and «that is so», or by nodding or other socially accepted gestures of assenting. For the sake of simplicity, we shall in this chapter assume that Q responds verbally and in such a way that we may with great certainty infer that Q regards as tenable that proposition that he believes P tries to convey to him.