Concerning Genus and Species.

The question on which Peter Abelard (c. 1079–1142) originally made his name and indeed the question that engaged philosophers at the fledgling school at Paris was the so-called problem of universals (common terms like "animal" or "man"). Sparked by a casual remark by Boethius in one of his commentaries on Aristotle's logic ("concerning genus and species, whether they have real existence or are merely and solely creations of the mind … on all this I make no pronouncement"), the debate raged for nearly half a century. John of Salisbury (c. 1120–1180), a Paris graduate, visited his alma mater twenty years after he had left for England and remarked that the Paris masters in the intervening years had made no progress in resolving the conundrum concerning universals.

Realism and Nominalism.

The debate surrounding universals focused on the problem of whether universals, essential...