Because both substances share the quality of producing intoxication, and intoxication is the very factor that renders the original substance unlawful, while it is likewise present in the derivative case.

Through this common quality one affirms that every intoxicant is forbidden; and by the same token one affirms—​a fortiori—​that intoxication itself is the ground of the prohibition. Indeed, establishing the matter by means of analogical reasoning is easier, for the ruling on the original already bears witness to its unlawfulness.

Thus the ruling is known to apply to a given individual instance. Yet in analogical reasoning it is not enough merely to establish the ruling for one of the two particulars and then transfer it to the other on the basis of a shared feature for which no proof has shown that it entails the ruling, as some mistaken people imagine. Rather, one must know that the element common to both necessarily entails the ruling. That common element is the middle term—what the jurists and the scholars of legal theory refer to when they demand evidence that the attribute in question exerts an effective influence on the ruling.

This is the greatest question posed against analogy, and its answer is most often required in order to validate the analogy.

An objector may deny the presence of the attribute in the original case, or deny the ruling in the original, or deny the attribute in the branch, or deny that the attribute is the causal factor behind the ruling. He may say, “I do not concede that the shared attribute you have mentioned is itself the cause, or even an indicator of the cause.” In that event one must produce evidence for the causal link—whether from an explicit text, consensus, the method of elimination and classification, considerations of suitability, or the principle of concomitance, according to those who employ it. Whatever demonstrates that the shared attribute necessitates the ruling—either as the cause itself or as evidence of the cause—shows that the middle term entails the major term and thereby verifies the correctness of the major premise. If it establishes the cause, the proof is a causal demonstration; if it establishes only an indicator of the cause, it is an evidentiary demonstration. And if the proof yields only likelihood and not certainty, then the major premise of that syllogism remains merely presumptive—​and this is perfectly clear.

For this reason many jurists employ in jurisprudence the inclusive syllogism, just as in rational disciplines the analogical syllogism is employed—​even though, in essence, each is nothing other than the other.