פירוש על שבועות 3:8

אם לא ראיתי גמל פורח באויר – meaning to say, they will forbid all produce/fruit that is in the world if I didn’t see, etc. [i.e., a camel flying in the air].

נחש כקורת בית הבד – like the shape of the beam of an olive press and its form. As if like the thickness of the beam of olive press, this would not be an oath taken in vain/false oath, asserting something impossible, where there a lot [of them].

At the end of the previous mishnah we were introduced to the concept of a vain oath, which is forbidden in Exodus 20:7, one of the verses of the Ten Commandments. The punishment for intentionally swearing in vain is lashes and for unintentional swearing in vain there is no punishment. Our mishnah lists four different types of vain oaths.

שבועה שלא נדיעך – it is the abrogation/nullification of a commandment, for he is obligated to testify as it states (Leviticus 5;1): “he does not give information – so that he is subject to punishment.”

What is a vain oath?
If he swore that which is contrary to the facts known to people, saying of a pillar of stone that it is of gold; or of a man that he is a woman; or of a woman that she is a man. If one swears about something that is obviously false, for instance if he looks at a pillar of stone and swears that it is gold, then he has taken God’s name in vain by swearing in vain.

If he swore concerning a thing which is impossible, [for instance if he said,] “If I have not seen a camel flying in the air”, or “If I have not seen a serpent as thick as the beam of the olive press”. Similarly, if he swears by something that cannot happen, for instance he swears that he saw a camel fly in the air, he has also sworn in vain.

If he said to witnesses, “Come and bear testimony for me”, [and they replied,] “We swear that we will not bear testimony for you”. According to Leviticus 5:1, if a person has been witness to an event he is obligated to testify. If a person asks another person to testify and he has testimony to give, and he swears that the he will not testify, then he has sworn in vain. This example actually can fit into the example in the next section, one who swears not to observe one of the commandments. Since testifying is a positive commandment one who swears not to do so has sworn in vain.

If he swore to annul a commandment, [for example] not to make a sukkah, or not to take a lulav, or not to put on tefillin. These are vain oaths, for which one is liable, for intentional transgression, lashes, and for unintentional transgression one is exempt. One who swears not to observe one of the commandments has sworn in vain.

Questions for Further Thought:
• Why does the mishnah consider all of these oaths to be in vain?
• What is the difference between a false oath and a vain oath?