Averah Matzah

The Mishna in Pesachim 35a lists all the things that one can’t use to fulfill their obligation of matzah.  Included on the list is tevel.  The Gemorah 35b explains it isn’t good for the mitzah because one can only fulfill the obligation it the issur of chametz would apply to it as opposed to what is prohibited because of tevel and this rule is based upon a derasha.  The Gemorah explains that the ברייתא that gives this explanation holds אין איסור חל על איסור and hence because there is a prohibition of tevel the prohibition of chametz doesn’t take effect.  Presumably, since we hold איסור חל על איסור באיסור מוסיף it should come out that you can fulfill your obligation with tevel.  However, the Rif and Rambam rule that you can’t fulfill your obligation.  Why?  The Rishonim explain because of the principle of מצוה הבא בעבירה.  If this understanding is correct, why didn’t the Gemorah give this reason and why do we need a specific derasha here if there is a general pesul?  Tosfos Sukkah 9a says that the rule of מצוה הבא בעבירה is only a Rabbinic pesul and the Gemorah is giving an explanation that will make it a Torah pesul. 

Another answer the Rishonim cite in the name of Tosfos (cited in Rabbenu Peretz here) suggest that the only time we find the pesul of מצוה הבא בעבירה is regarding mitzvot that come to be מרצה such as korbanot, lulav (has an aspect of prayer and hallel to it.)  However, matzah that isn’t coming to be מרצה there is no pesul of מצוה הבא בעבירה.  The Rishonim ask questions on this interpretation from examples of מצוה הבא בעבירה even when the mitzvah isn’t coming לרצות.  (According to this interpretation it should come out we don’t hold there is מצוה הבא בעבירה in this case.)

The Ramban entertains a possibility that there is no problem of מצוה הבא בעבירה here because the person has the ability to fix the issur by separating the proper tithes.  What is the explanation of this sevarah, what does it help that you could remove the issur, right now it is assur?  The Achronim explain the yesod of the pesul מצוה הבא בעבירה is that the חפצא is a חפצא of averah.  Regarding tevel what defines it as a חפצא של עבירה isn’t because of the averah done to it, there was no averah done to it, rather it is defined that way because the מצוה is performed via an averah.  The Ramban holds if one can avoid the issur by tithing, it isn’t considered as if the averah is enhancing the mitzvah because it can be avoided. 

It is interesting to note that Rashi on the Mishna explains the pesul based upon a suggestion of the Gemorah that the ברייתא could even fit with the Rabbis that it comes to exclude anything that has an issur besides that of chametz alone.  The Gemorah rejects this explanation because there is no mention of “only” in the ברייתא.  So why does Rashi cite a rejected pshat?

 However, the Meiri says that the rejection of the Gemorah is merely a דחוי but really that answer stands.  This would be a different explanation as to why we would rule that you can’t fulfill your explanation and we don’t have to come up with a new reason of מצוה הבא בעבירה (see Birchat Mordechai Pesachim #19.)