Question: The Gemara says you can't learn that apples can be used for an eiruv from the work "kol" because there may be an exception, but you can learn from the fact that mistama anything that can become tamei can be used. Why is the second limud stronger than the first one?
The first Limud is a "Klal," a general principle, and in such a form of Limud there are exceptions ("Yotz'im Min ha'Klal"), as the Gemara cites from Rebbi Yochanan (Ein Lemeidin Min ha'Kelalos). The second Limud is derived from a comparison of the cases mentioned in the Mishnah (this is similar to a Hekesh, which is applied to verses in the Torah). We do not find exceptions to such a comparison, for if there were exceptions it would not have been appropriate for the Mishnah to equate the two cases.
Be well,
M. KORNFELD