  Strictly speaking, ḥads is the revelation—some would add instantaneously—of the middle term of the syllogism, leading to an infallible conclusion. In practice, though, it had much wider application and less precise definition. Rare indeed is the case, when ḥads is cited as the source of knowledge, that the writer will display the full syllogism and specify the middle term (see Langermann 2005, 286–302, and Gutas 2001). In effect, it is of the same species as the “revelations” by which Avicenna learned of his own existence (and indeed the great bulk of his education) and, like that Avicennan moment, it shifted epistemology in the direction of a reliance upon a person’s sense of security in his personal illuminations . In the work of later thinkers, including Ibn Kammuna, the evaluation of ḥads served to legitimize alchemy and astrology and, more generally, to blur the distinction between demonstrative knowledge and revelation.