Reply To: Chidushim on Daf Yomi Shabbos 30

שבת עג,א

The mishna says that there are forty minus one avos malochos, asks the Tosfas Yom Tov why does it not say thirty nine. He answers that there are really forty malochos as sewing requires a knot but it is not counted being part of the malochoh of sewing.
The mishna refers to the individual doing the work whereas the Rambam refers to the work itself הזורע vs הזריעה? Answers the Magen Avos by Rav Mordechai Binet ztz”l that the Rambam follows his view that מלאכה שאינה צריכה לגופה work not done for its own purpose is also chayev so it is not dependent on the person doing it. The difference between a פסיק רישא is as explained by Rabbenu Avraham, the son of the Rambam as quoted by the Kesef Mishna, by the former he is mechaven but not for the purpose done in the mishkan whereas the for the latter he is not mechaven at all and the melacha happens by itself.
Asks the Machtzis Hashekel O’CH 278, then why does Rabbi Shimon pater מלאכה שאינה צריכה לגופה when you are mechaven? He answers that since he is not mechaven for the purpose done in the mishkan, it is considered a reverse kavono and it is worse than having no kavono at all.