because the ruling is based on the effective cause: if the original case and the subsidiary case share the same effective cause, they share the same ruling; otherwise, they do not.

The distinction, according to them, is that a dog’s saliva contains a tapeworm that is harmful to human beings. When the dog laps from a vessel, it separates from its saliva into the vessel; then, if someone uses it afterward, it attaches itself to the person’s stomach and perforates it. Nothing destroys it except soil.

But if this effective cause is medically established, is it absent from the dog’s urine and droppings? This must be investigated. If it is established that it is absent, then this view has some basis for consideration. Otherwise, the more cautious position is that held by the majority of jurists: if you purify it seven times, one of them with soil, no one will say that you have erred. But if you do not purify it with seven washings, one of them with soil, then there are those who will say that you have erred and that the vessel has not been purified.

…

His statement, “and a pig”: the pig is a well-known animal, characterized by a lack of protective jealousy, foulness, and eating filth. Its flesh contains harmful germs, and it has been said that fire does not succeed in killing them. This is why the Lawgiver prohibited it.

The jurists, may Allah have mercy on them, likened its impurity to that of the dog, because it is more foul than the dog and thus more deserving of the same ruling.

But this is a weak analogy, for the pig is mentioned in the Quran and existed during the lifetime of the Prophet ﷺ, yet no report has come likening it to the dog.

The correct view is that its impurity is like that of other impurities: it is washed as the rest of impurities are washed.

Soapwort and the like suffice in place of soil.

His statement, “Soapwort and the like suffice in place of soil”: soapwort is a tree.