This article studies the advances made in the logic of Renaissance physiognomy from the state of the subject in antiquity and the Middle Ages. The properties and accidents of the human body are investigated in the context of the signs selected by physiognomers, whether univocal or in syndromes, strong or weak in character, negative or positive, consistent with each other or contradictory. When these signs are translated into propositions, the construction of argument which flows from them is shown to ut plurimum reasoning, in which an element of quasi-mathematical proto-probability and hermeneutical thinking (in the treatment of ambiguity and obscurity) may be detected. These allow the question "is x more likely to be the case than y or z?" to be answered through a variety of procedures. Renaissance physiognomy is shown to be a discipline in which a novel combination of rational procedures come together, and a site of conceptual change in respect of property and accidence.