The Topics is is the fifth of Aristotle's six texts on logic which are collectively known as the Organon ("Instrument"). The Topics constitutes Aristotle's treatise on the art of dialectic—the invention and discovery of arguments in which the propositions rest upon commonly-held opinions or endoxa. Topoi are "places" from which such arguments can be discovered or invented. In his treatise on the Topics, Aristotle does not explicitly define a topos, though it is "at least primarily a strategy for argument not infrequently justified or explained by a principle."