Question

In the laws of salting, there are many factual claims that serve as the basis for the laws: 1. For example, something that is occupied with expelling does not have the capacity to absorb. 2. A difference in how a piece of meat absorbs blood—between visible blood, blood contained in the limbs, or residual blood after salting. 3. Fish expel all their juices before the bird finishes expelling its blood. Based on these assumptions, Jewish laws are established regarding meat that was salted a second time, the need to rinse before and after salting, and more. Also, the disputes among the medieval authorities (Rishonim) are disputes about facts—for example, Rabbenu Tam, regarding salting several pieces of meat together, holds that during salting the blood flows off smoothly and therefore is not absorbed; in contrast, other medieval authorities hold that the blood is indeed absorbed, but then expelled. What is the logic of establishing Jewish law on the basis of unproven facts? Especially since it is also unclear on what basis each commentator decides when absorption does occur and when it does not.