The sayfa of the mishna explains that the raisha does not mean that temurah is permitted. The gemara asks on the raisha, as if the sayfa does not exist. The maskana of the gemara explains that the raisha means that everyone has the ability -- it takes effect and is mechayev malkos.
1) Why does the gemara ignore the sayfa, only to say esentially the same thing as the sayfa m'svara?
2) If the intent is that the words of the raisha by themselves should be understood to mean that the temurah takes effect, why is the sayfa even necessary?
Thanks & Ksiva, V'chasima Tova,
Dovid Hoffman, Baltimore, USA
1) The Gemara is not ignoring the Seifa. It is asking a contradiction between the Reisha and the Seifa. Even if one is not actually Gores the words "...Ela she'Im Hemir Mumar" in the question of the Gemara (SHITAH MEKUBETZES #3), the Gemara is clearly asking a contradiction from the Reisha to the Seifa. The Reisha of the Mishnah implies that one can be Memir, since "ha'Kol Memirin" implies that it may be done l'Chatchilah. The Seifa, though, says that one cannot make a Temurah l'Chatchilah, rather Temurah takes effect only b'Di'eved , if one transgresses the prohibition of making a Temurah.
2) The Seifa was written to prevent misinterpretation of the Reisha. In order that an unknowledgeable person not read the Reisha to mean "ha'Kol Memirin l'Chatchilah" (as the expression "ha'Kol xxx" normally means), the Mishnah spells out that it is not permitted l'Chatchilah.
A bigger question would be the inverse: Why did the Mishnah write "ha'Kol Memirin" in the Reisha? Rather than writing "ha'Kol Memirin" and then correcting the misinterpretation that this expression causes, let the Mishnah write an expression that does not imply l'Chatchilah!
According to Tosfos (DH Ha Gufa, and in the beginning of Chulin), the Gemara is addressing this question as well. Its answer is that "ha'Kol Memirin" teaches either that Temurah takes effect even if one makes a Temurah b'Mezid, or that a Temurah made by women is brought on the Mizbe'ach.
(Note that according to Rashi in Chulin, as cited by Tosfos here, this question does not begin; see Tosfos ibid.)
Kesivah va'Chasimah Tovah,