(a)
One of the various general forms of argument employed in probable as distinguished from demonstrative reasoning, denominated by Aristotle topoi (literally, places), as being the places or sources from which arguments may be derived, or to which they may be referred; also, a prepared form of argument, applicable to a great variety of cases, with a supply of which the ancient rhetoricians and orators provided themselves; a commonplace of argument or oratory.
(b)
pl. A treatise on forms of argument; a system or scheme of forms or commonplaces of argument or oratory; as, the Topics of Aristotle. "These topics, or loci, were no other than general ideas applicable to a great many different subjects, which the orator was directed to consult." "In this question by (reason) I do not mean a distinct topic, but a transcendent that runs through all topics."