This kind of reflection yields knowledge just as the eye’s vision yields knowledge of what it sees; hence it does not oppose knowledge. It is reflection upon the evidence itself—like one who studies the Qur’an and the Sunnah and thereby learns the ruling—whereas the first kind is reflection upon the ruling, like someone who examines a legal question in order to extract its proof from the Qur’an and Sunnah.

We therefore say: it is obvious that the heart’s recognition that a predicate belongs to a subject—that is, affirming an attribute for the thing described, such as the prohibition of an intoxicant—may be obtained by means of a middle term. One knows, for example, that this drink is wine, and he also knows that wine is forbidden; this is qiyās al-shumūl, the syllogistic form of qiyās.

Knowledge may also be reached in a different way: a person may see that the intoxicant is equivalent to grape wine with respect to the very cause of prohibition and so judges them equal in ruling; this is qiyās al-tamthīl, analogy. Or he may discern in the drink the very harm found in wine and therefore pronounce it forbidden in order to ward off that harm; this is qiyās al-taʿlīl, causal inference.

Both analogical qiyās and causal qiyās fall under the general category of qiyās. When establishing the ruling for a subsidiary case, however, one may need to link it to a specific principal case, doing so either by presenting the common factor or by nullifying any purported difference. Presenting the common factor—the effective cause (ʿilla) of the ruling in the principal case—is called qiyās al-ʿilla. What merely points to the cause is qiyās al-dalāla; this combines both analogy and causal inference. If the extension is made by eliminating any relevant difference while the precise cause is unknown, this is analogy without causal inference. Conversely, evidence may establish that a given attribute necessarily entails the ruling even though no particular principal case is cited; this is causal inference, and it resembles the syllogistic form.

Syllogistic qiyās and analogical qiyās are mutually inseparable: whatever is expressed in one form can be expressed in the other. The syllogistic form always contains a repeated middle term, and that term is precisely the nexus of the ruling in analogical qiyās—the common element that unites the principal case with the subsidiary. For example, when one says, “Nabīdh is forbidden by analogy with wine, because it possesses the same intoxicating potency,” he has provided an illustration of both forms of qiyās.