Peter Abelard was a French philosopher and logician, the most celebrated teacher of his generation, and a man whose personal catastrophe has tended to overshadow his work.

Universals

The twelfth-century dispute asked whether general terms name real things. Realists held that humanity exists over and above individual humans; nominalists held that only individuals exist.

Abelard's answer took a middle route. What is shared is not a thing but a status — the way individuals are, which the mind grasps as a common concept. Universals are neither free-standing entities nor arbitrary noises. The position dominated until the realism of the next century revived the alternative. See universals and nominalism.

Ethics of intention

His Ethics, subtitled Know Yourself, argues that sin lies in consent rather than in the act or the desire. A person who desires wrongly and does not consent has not sinned; someone acting in genuine ignorance of the wrong is not culpable in the same way.

This relocates morality inward, which was a substantial break from a penitential system organized around acts and their tariffs, and it anticipates the emphasis later found in Kant.

Sic et Non

He compiled 158 theological questions and set the authorities against each other on every one, without resolving them. The point was pedagogical: the apparent contradictions force the reader to attend to the terms, the context, and who is saying what. It is the direct ancestor of the scholastic method of disputation that Aquinas later used, with the resolution supplied.

Héloïse

His relationship with his student Héloïse d'Argenteuil, her forced entry into a convent, and his castration by her relatives are the most-told story about him. Their surviving correspondence is a substantial philosophical text in its own right, and Héloïse's letters argue positions on intention and love that hold their own against his.