The shiur for mitzvos and issurim that entail achila is a k'zayis, as ain achila p'chusa mi'kzayis. However, in truth the shiur k'zayis is not just a din in achila, but is the baseline shiur for all mitzvos/issurim until proven otherwise.
The first Mishna in Beitzah has a machlokes Beis Hillel and B"Sh whether the shiur bal yeira'eh and bal yimatzei for chamtez is k'zayis, like se'or, or whether the shiur is larger. The gemara explains B"Sh:
מאי טעמייהו דב"ש א"כ לכתוב רחמנא חמץ ולא בעי שאור ואנא אמינא ומה חמץ שאין חמוצו קשה בכזית שאור שחמוצו קשה לא כל שכן שאור דכתב רחמנא למה לי לומר לך שיעורו של זה לא כשיעורו של זה
Meaning, all things being equal, you would assume the shiur is k'zayis.
Why? If the only reason the shiur achila is a k'zayis is because ain achila p'chusa mi'kzayis, what does that have to do with bal yeira'eh and bal yimatzei?
QED that k'zayis is a baseline shiur, not just a shiur of achila.
See Minchas Chinuch 89 who points out the same with respect to the issur of lo tischat al chameitz dam zivchi being k'zayis.
Chameitz is only things that are ra'ui la'akhila, and machametzes -- ra'ui la'akhilas kelev. So, if ein akhilah pechusa mikezayis, then something that small isn't ra'ui la'akhilah by human or dog. Seems like a clear connection to me.
ReplyDeletechameitz is asur b'mashehu but is mutar if it is not ra'uy l'achila. you are confusing eichus and kamus.
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ReplyDeleteThe Ran at the beginning of Pesachim suggests that Bal Yiraeh/Bal Yimatzei are a kind of syag de'oraysa to achila, since chametz is commonplace the rest of the year. So that would explain a connection between those issurim and kezayis.
ReplyDeleteAnd notwithstanding your comment above, I think Micha Berger is correct to note that ra'ui le achila, a requirement for BYBM, connects them to achila as well. (In fact, that is support for the Ran's position. If there is no issur achila, there is no BYBM either.)
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Delete>>>The Ran at the beginning of Pesachim suggests that Bal Yiraeh/Bal Yimatzei are a kind of syag de'oraysa to achila
DeleteCan you kindly point me to which Ran you are referring to?
If the geder ha'mitzvah is a syag, then there should be no B"Y when there is no issur achila and vice versa. Aside from the distinction I mentioned above (case of ma'shehu), a few more distinctions: taaroves is assur b'achila, but not clear that there is BY; chameitz on erev pesach; chameitz she'aino yadu'a according to some shitos would be a problem of BY but obviously there is no chance of eating something you don't know about.
Parshas ha'shavua b brought to mind another shiur k;zayis that has nothing to do with achila: shiur haktara is k'zayis. (Though maybe that is not a shiur d'oraysa.)