The fourth point is that, when the Lawgiver’s words do not indicate the effective cause of a ruling, analogy is valid only if we examine the attributes of the original case and find that none is suitable as the effective cause except the particular attribute identified. Whenever we establish the effective cause in the original case through suitability, concomitance, or consistent resemblance—for those who accept the latter—such examination is indispensable. If the original case has two suitable attributes, it is impermissible to say that the ruling rests on one rather than the other.

It is well known that the revealed texts and scholarly consensus establish that eating, drinking, sexual intercourse, and menstruation invalidate the fast. The Prophet, peace and blessings be upon him, forbade anyone performing ablution from drawing water deeply into the nose while fasting. Their analogy with drawing water into the nose is their strongest argument, as noted above, yet it is a weak analogy. When someone draws water in through his nostrils, it descends into his throat and internal cavity, producing the same effect as drinking through the mouth: his body is nourished by that water, his thirst is quenched, and the food in his stomach is digested, just as happens when he drinks water. Even without a revealed text concerning this, reason would establish that it belongs to the same category as drinking. The two differ only in whether the water enters through the mouth, and that difference has no bearing on the ruling.

Indeed, water merely entering the mouth does not invalidate the fast. Its entry into the mouth is neither something that invalidates the fast nor a constituent part of what invalidates it, since it has no effect in itself; it is merely a route to the fast being invalidated. The same does not apply to kohl, enemas, or the treatment of wounds penetrating a body cavity or reaching the membrane surrounding the brain. Kohl provides no nourishment whatsoever, and no one introduces kohl into his internal cavity through either his nose or his mouth.