 Something is readily believable (probabilis) if it seems true to everyone or to the most people or to the wise – and of the wise, either to all of them or most of them or to the most famous and distinguished – or to an expert in his own field, for example, to a doctor in the field of medicine or to a pilot in the navigation of ships, or, finally, if it seems true to the person with whom one is having the conversation or who is judging it. (Boethius, De topicis, 1180b28)