 The theory of properties of terms (proprietates terminorum) was the basis of the medievals' semantic theory. It embraced those properties of linguistic expressions necessary to explain truth, fallacy and inference, the three central concepts of logical analysis. The theory evolved out of the work of Anselm and Abelard at the turn of the twelfth century, developed steadily through the thirteenth and fourteenth centuries and was still undergoing changes in the fifteenth and sixteenth centuries. It is generally agreed that its early stages were closely bound up with the theory of fallacies, but as a general semantic theory, it developed in response to a variety of needs, and one mistake of modern attempts at interpretation is to seek a unique rationale of one notion or another. Each notion evolved continually, satisfying one need at one time and another at a later date, and often several conflicting needs at the same time. Another mistake is to try to map each notion seriatim onto corresponding notions in contemporary semantic theory, but although one can see analogies and similarities, none of the medieval “properties” matches exactly any modern notion.