Dear Rabbi Pearlman,

You were so helpful on the question on Makos, I figured I would ask you a question on another gemorah I just started learning since I finished Makos.

I started the sugya of Hoil in Masechta Pesachim from daf 46. Anyway on daf 47b the gemorah engages in a discussion regarding whether if someone is choresh on yom tov whether he can say "hoil vchazi lkisui dam tzipor"(since it is possible that he will need the earth for kisuy dam tzipor". The gemorah then says that the earth in it's case was full of stones and there is a whole give and take thereafter and that kisuy hadam in that case was inapplicable.

Tosfos on that daf in D"H "Ketisha Byom Tov Mi Shari" (4th Tosfos on the amud) says that the hava amina was that kisuy hadam is mutar because aseh doche lo saaseh. I am perplexed by this. Isn't the classic difference between an aseh doche lo saaseh and mitzvah habbah baverah in that by the former they come at the same time and by the latter the mitzvah results only after the averah. (An example of the ashe doche lo saaseh is by milah btzaraas. A mitzva haba bavera would be lulav hagazul.) Over here at the time he is plowing he is not doing the kisuy hadam. It is only a preparation for the kisuy hadam should he need to do it. So how can Tosfos say this is the hava amina of the gemorah? This would not be a case of aseh doche lo saaseh.

If you can help me on this question it would be much appreciated.

Thank You,

Shmuly