The Rambam (Shabbos 1:6) identifies cutting off the chickens head as the unique example of “psik reisha” — but it obviously isn’t. Rather, it is a melacha sheina tzericha legufa.
Please explain.
Answer:
The Kessef Mishnah (Shabbos 1:7) writes that the difference between eino miskaven and eina tzericha legufa is that in the former a person doesn’t intent any melacha to be done, and the melacha is done without intention, whereas in the latter there is intention for the melacha but not for its purpose. He cites this from Rabbi Avraham ben Ha-Rambam, in the name of the Rambam himself (see Kapos Temarim 33b).
Yet, this does not appear to be in line with the Rambam’s case, in which a person intends to cut off the head, but only for a different purpose.
Reading the Rambam, we see that the Rambam appears to maintain that this, however, is the classic case of pesik reisha. The Rambam doesn’t give an example of somebody dragging a bench where grooves will certainly be made, or similar cases. Rather, he gives the example of somebody who wants to do the melacha itself, only for a different purpose.
Thus, it is perhaps possible that the Rambam maintained that the case of a pesik reisha is in fact a case of eina tzericha legufa – a case where the intention is the melacha. In this the Rambam rules like Rabbi Yehuda, meaning that a person is chayav.
There is more room for iyun in this complex matter.
