  A singular term, such as a proper name or a demonstrative pronoun, is a term that signifies exactly one individual thing. The existence of singular terms raises various questions about how they function within a language. Do proper names have a sense as well as a referent? If they do have a sense, what is it, and how do they acquire it? How is this sense transmitted from one speaker to another? Is a demonstrative pronoun purely referential? If one believes in a language of thought, or mental language, as did many medieval thinkers, what is the mental correlate of a singular term? While medieval thinkers did not produce any treatises devoted to singular terms, their writings do contain answers to these questions, or at least, answers to similar questions that they themselves posed in the context of their own semantic theories. To discover medieval views of singular terms, one must consult a variety of sources from grammar, logic, metaphysics, and even theology. Priscian, the semantically-oriented grammarian who wrote at the beginning of the sixth century C.E., was particularly influential, and his views were repeated by many later grammarians, as well as by logicians and theologians. Porphyry’s Isagoge, or introduction to Aristotle’s Categories, was another important source, especially as his discussion allowed commentators to relate linguistic problems to metaphysical problems concerning the nature of the individual named by a singular term. Commentaries on Aristotle’s Categories discussed singular terms as examples of equivocal terms, those having more than one sense. Later in the Middle Ages and at the beginning of the sixteenth century, singular terms were discussed in treatises devoted to types of terms. Paul of Venice’s treatise is worthy of special mention here, despite the difficulty of construing many of his claims.  Because the use of singular terms was tied to singular concepts, they were also discussed in commentaries on Aristotle’s Physics, De anima, and Metaphysics. The commentaries of John Buridan (d. after 1358) provide the richest and most coherent medieval theory, and one which remained influential into the sixteenth century. During the sixteenth century, singular concepts remained a subject of discussion in commentaries on Aristotle’s Physics and De anima, but unfortunately the logicians who came after Domingo de Soto (1494–1560) reverted to a very cursory treatment of singular terms. We have to wait for the nineteenth and twentieth centuries for a rediscovery of some of the problems that had exercised John Buridan in the fourteenth century. 