one of the two premises. If the analogy proceeds by eliminating any relevant difference, a specific primary case is indispensable, for the shared attribute is the equality and equivalence of the two cases. This elimination of any relevant difference is the middle term. If the analogy proceeds by identifying the cause, mentioning the primary case may be unnecessary when establishing the attribute’s causal character does not depend on it. But if establishing its causal character requires the primary case, that case is mentioned because it completes the evidence establishing that the shared attribute is the cause; this is the major term.

Those who distinguish between analogical and syllogistic reasoning have sought to show that one of them is conjectural in particular subject matters. Yet those subject matters that yield only conjecture in analogical reasoning likewise yield only conjecture in syllogistic reasoning. Conversely, when they employ it in matters in which syllogistic reasoning yields certainty, analogical reasoning also yields certainty. Indeed, the certainty it yields is even more evident there.

Thus, if the following syllogism is stated:

“Every human is an animal, and every animal is a body; therefore, every human is a body,”

“animal” is the middle term. It is also the shared attribute in analogical reasoning, expressed by saying: “A human is a body by analogy with a horse and other animals,” for those animals’ being animals necessarily entails their being bodies.

If the causal basis of the judgment in the primary case is disputed, and someone objects, “We do not concede that being an animal necessarily entails being a body,” this is a dispute over the statement, “Every animal is a body.” For when the attribute shared by the primary and secondary cases is called a cause, what is meant is simply that which necessarily entails the judgment, whether it is the cause that necessitates the judgment’s existence in external reality or something that necessarily entails it.