A man who makes an assertion puts forward a claim—a claim on our attention and to our belief. Unlike one who speaks frivolously, jokingly or only hypothetically (under the rubric ‘let us suppose’), one who plays a part or talks solely for effect, or one who composes lapidary inscriptions (in which, as Dr Johnson remarks, ‘a man is not upon oath’), a man who asserts something intends his statement to be taken seriously: and, if his statement is understood as an assertion, it will be so taken. Just how seriously it will be taken depends, of course, on many circumstances—on the sort of man he is, for instance, and his general credit. The words of some men are trusted simply on account of their reputation for caution, judgement and veracity. But this does not mean that the question of their right to our confidence cannot arise in the case of all their assertions: only, that we are confident that any claim they make weightily and seriously will in fact prove to be well-founded, to have a sound case behind it, to deserve—have a right to—our attention on its merits.