Someone argues: “The particular cause is absent, therefore the legal ruling is absent.” This is valid as a necessary inference only if evidence shows that the ruling's cause is exclusive to that one factor. If another recognized cause remains possible, the absence of the first cannot negate the ruling categorically.
In ablution discussions, “nothing exited through two designated passages, so no invalidation occurred” raises exactly this question: are all relevant invalidating causes confined to those passages? If exclusivity is unproved, the inference is too broad.
Distinction: “This cause does not establish the ruling” is not the same as “no cause can establish the ruling.”