Inference and Enthymeme in William Ockham

Ockham classifies inferences based on their terms and based on the propositions' quantity, quality, and modality. He also distinguishes between simple and as-of-now inferences, between inferences that hold good by extrinsic (valid in virtue of a logical rule) or by intrinsic (valid in virtue of an additional premise) means, between formal and material (valid in virtue of the meanings of its terms) inferences. From the lecture of Summa Logicae, Ordinatio, and Expositio super Libros Elenchorum Aristotelis, it seems that Ockham includes enthymemes under the rubric of formal inferences by indicating how they can be transformed into a fully stated syllogism adding a premise. The added premise may be either necessary or contingent. Ockham refers to the enthymeme or an enthymematic procedure in the fallacy of the form of expression, the fallacy in an absolute sense or for a specific aspect, and the consequent's fallacy.