daf bit: Shevuot 3
Tractate Shevuot is about oaths and begins with a mishna saying: oaths are of two kinds, subdivided into four. (The rabbis are big on numbers and divisions of things.) The g'mara gives an example: two are "I shall eat" and "I shall not eat"; four are "I have eaten" and "I have not eaten". Rabba says that the latter, if false, are clearly punishable by lashes, for the speaker knowingly transgressed (saying he had not eaten when he did, for instance). But, the g'mara asks, if he says "I will eat" and he does not eat, why should he be liable, asks an anonymous tanna? Can you be liable for inaction? R. Yochanan and Reish Lakish do not hold him liable; if he says "I swear I shall eat this loaf today" and he does not, they do not hold him liable to lashes. R. Yishmael, however, says he is liable in all four cases. (3a-b)
I don't see a resolution in the g'mara here, but it looks like this discussion goes on for many more pages in many threads, so it might come back later.
I believe based on discussions in the previous tractate, but am not certain, that the reason one might not be liable for not eating (after saying "I will eat") is because it is hard to give a proper warning. If someone said "I will not eat" and you see him picking up food, you can warn him of the punishment if he eats. If he says "I will eat" and he passes up food now, you don't know that he isn't going to eat later; "I will eat" does not bind him to a particular time. So if it's a minute before the end of the day and he hasn't eaten you can warn him, but that's about it.
This tractate is called "oaths" but two of these examples sound like vows to me rather than oaths. (There's another tractate, Nedarim, that addresses vows.) Is there a technical distinction between the two that is consistent with today's text?

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I agree on "vows" versus "oaths". Perhaps that is the distinction they are attempting to address: we may call this an "oath", but it isn't the same thing as taking oath that your words are true. For the past, we can take oath that such and such was true. For the future, we can only take oath of our intent now.
Does the section on vows come later? Maybe this is leading up to that?
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Looking at it a different way: a man who can take *oath* that something shall happen in the future, that's prophecy! So, unless we are going to say "This man is a prophet: he has predicted that thus and thus shall happen in the future, for it is God's Will", he's just making a statement of intent.
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(Nedarim was a few tractates ago. Not that ordering is strongly significant...)
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