a writer, without feeling obliged to cite both premises in order to validate his inference. They object, saying: “Two premises are indispensable. If only one of them is voiced, the speaker relies on the addressee’s awareness of the second, so he leaves it unspoken—yet not because it is superfluous.”
We answer: We do not find two universal premises by which the truth of a conclusion is established. Suppose someone says,
“Substance pertains to every living thing,
and life pertains to every human being;”
then the conclusion would read, “Substance pertains to every human being.” In the mind, however, the statement “Substance pertains to every living thing” carries exactly the same weight as saying “Substance pertains to every human being.”
I say: The sense is this: when we affirm, “Every human being is living, and every living thing is a substance,” just as they affirm, “Every human being is an animal, and every animal is a substance or a body,” it makes no intellectual difference whether we know that every human being is a substance or body or that every animal is a substance or body. Whoever knows the latter already knows the former.
His purpose is to show that they cannot supply two primary, self-evident premises by which to prove any disputed point that actually requires demonstration. One of the two—or both—must be non-evident. If, by hypothesis, both are self-evident, one of them alone suffices, as the example shows. If one premise is theoretical, that is the one that needs to be proven; and if both are theoretical, then both must first be proven, as though there were three premises—the point in need of proof and the premises by which proof is made. In reality, one begins reasoning only with what is immediately manifest in itself, namely the axioms.
He continues: “In scientific inquiry they never find that a sought-after conclusion depends on two premises that are each self-evident; were that the case, one of them would be enough.”
He also says: “Let them produce two primary premises that require no antecedent proof, by which they can establish a contested matter, and whose acceptance in the intellect is more obvious than that of the conclusion. If they cannot, their claim collapses.”
Abū Muḥammad al-Ḥasan ibn Mūsā al-Nawbakhtī adds: “I questioned a number of their leading figures…"