Much of the recent attention of historians of medieval logic has focused on medieval semantics. Just as prominent in medieval logical treatises, however, is the topic of inference, and a great deal of sophisticated work was done in this area, particularly by the fourteenth-century Latin authors on which this chapter will concentrate.

KINDS OF INFERENCE

Inferences are the building blocks of scholastic thought, and it is scarcely possible to read a paragraph of later medieval philosophy without encountering the terminology in which inferences are couched. Indeed, nothing is more familiar from scholastic texts than phrases such as this: Patet consequentia, antecedens est verum, ergo et consequens (‘The inference is seen to hold, the premise is true, so the conclusion is true too’). The term consequentia translates most readily as ‘inference,’ but what counts as an inference, to say nothing of what counts as a valid inference, is a thorny question. Even as good a logician as John Buridan may describe a consequentia as a molecular proposition (propositio hypothetica): “Now an inference is a molecular proposition, for it is composed from several propositions conjoined by the expression ‘if’ or by the expression ‘therefore’ or something similar” (Tract. de consequentiis I.3, ed. Hubien, p. 21). Yet when one argues: ‘This is false, Socrates utters it, so it follows that Socrates utters a falsehood,’ there is no conditional in this inference (consequentia), but two premises (antecedentia) and a conclusion (consequens). The same is true of syllogistic inference, in which there are two premises and a conclusion.