"Anumāna" (अनुमान) means inference. It is described as reaching a new conclusion and truth from one or more observations and previous truths by applying reason. Observing smoke and inferring fire is an example of "Anumana". In all except one Hindu philosophies, this is a valid and useful means to knowledge. The method of inference is explained by Indian texts as consisting of three parts: "pratijna" (hypothesis), "hetu" (a reason), and "drshtanta" (examples). The hypothesis must further be broken down into two parts, state the ancient Indian scholars: "sadhya" (that idea which needs to proven or disproven) and "paksha" (the object on which the "sadhya" is predicated). The inference is conditionally true if "sapaksha" (positive examples as evidence) are present, and if "vipaksha" (negative examples as counter-evidence) are absent. For rigor, the Indian philosophies also state further epistemic steps. For example, they demand "Vyapti" - the requirement that the "hetu" (reason) must necessarily and separately account for the inference in "all" cases, in both "sapaksha" and "vipaksha". A conditionally proven hypothesis is called a "nigamana" (conclusion).