 Many classical Indian philosophers held that apparent certification may not be enough to warrant belief in some instances. Even if our beliefs/cognitions have indeed been generated by processes that would be counted knowledge sources did they not face counterconsiderations, in facing counterconsiderations—in being reasonably challenged—they are not trustworthy and do not guide unhesitating effort and action.  There is a social dimension to knowledge, where reasoning reigns resolving controversy in ways over and above the sources. These are the ways of tarka, “hypothetical” or “suppositional reasoning.” Paradigmatically, tarka is called for in order to establish a presumption of truth in favor of one thesis that has putative source support against a rival thesis that also has putative source support, a thesis and a counterthesis both backed up by, for example, apparently genuine inferences (the most common situation) or by competing perceptual or testimonial evidence. By supposing the truth of the rival thesis and (in Socratic style) showing how it leads to unacceptable consequences or breaks another intellectual norm, one repossesses a presumption of truth, provided—the classical epistemologists never tire of emphasizing—provided one’s own thesis does indeed have at least the appearance of a knowledge source in its corner. The consensus across schools is that such arguments are not in themselves knowledge-generators, but they can swing the balance concerning what it is rational to believe.