By means of their respective balances one determines the quantity of such objects; in the same way, one knows that this dry measure equals that one by using its own balance—namely, measuring vessels. Likewise, we ascertain that one span of time matches another by the instruments with which time is reckoned: sundial shadows, the regulated flow of water or sand, and the like. Again, we confirm that this item is as long as that by its balance, the measuring rod. In short, between every pair of similar things there must exist a shared, universal standard by which one recognizes their equality.

So too with derivative legal rulings that are analogically linked to their roots, whether in revealed or rational matters: they are known through the balances common to both, that is, the unifying attribute called the “middle term.” Thus, when we know that God has forbidden grape wine because it diverts people from the remembrance of God and from prayer and foments enmity and hatred among the believers, and we then observe that fermented drinks made from wheat, barley, rice, and the like share that very overarching quality—the effective cause of the prohibition—this common factor becomes the balance God has placed in our hearts. By means of it we weigh one against the other, judge them alike, and refuse to differentiate between equivalent things. Sound analogy, therefore, forms part of the justice that God, exalted be He, has commanded.

Whoever possesses knowledge of universals without acquaintance with a particular instance holds the balance alone. Yet the purpose of the balance is to weigh things that exist outside the mind; without concrete particulars the universals would have no practical import, just as a balance would be useless were there nothing to weigh.

There is no doubt that when one of the two items is actually brought forth and compared with the other by means of the balance, the weighing is more complete than when the balance—i.e., the universal, shared description in the mind—merely weighs whatever individual happens to be present. That too is a valid weighing, and it is the better way, for when you weigh with the standard weight