 Gaṅgeśa, like other Naiyāyikas, also works with the distinction between the necessary and the sufficient, sufficient causality being a whole bundle of causal conditions, including general ones such as time and space. A source of knowledge is a process of knowledge generation, and each has a distinct “trigger.” A trigger is that instrumental cause which, when all the other causal conditions necessary for an effect are in place, brings it about. The trigger of perceptual knowledge is said to be connection of a sensory organ with an object to be known. The trigger of knowledge by inference is said to be reflection on a property of an object as pervaded by—invariably associated with—another property, the former called the prover—the pervaded—and the latter the probandum—the pervader. The trigger of testimonial knowledge is said to be the statement of a trustworthy expert as comprehended by the hearer, a trustworthy expert being defined as someone who knows the truth and wants to communicate it faithfully, without lying or deceiving. Causal relations are especially important because knowledge of the occurrence of an effect allows the knower to infer any one or more of its necessary conditions, as perception of smoke rising from a mountain allows one to infer fire. Furthermore, recognizing a particular knowledge source by its trigger is one way to certify a result, an instance of testimonial knowledge for instance.