After collecting leaven on the night of the 14th of Nisan, one is still permitted to eat it all the way through the morning, before the remainder is burned. A mishnah on today’s page gives more precise time parameters:
Rabbi Meir says: One may eat leaven the entire fifth hour of the 14th of Nisan, and one must burn it at the beginning of the sixth hour.
Rabbi Yehuda says: One may eat the entire fourth hour and one places it in abeyance for the entire fifth hour, and one burns it at the beginning of the sixth hour.
The rabbis divided the day (from sunup until sundown) into twelve equal parts, or “hours.” (In the winter, when there was less daylight, these hours were shorter and, likewise, in summer they were longer.) In this mishnah, Rabbi Meir allows us to eat leaven on the 14th of Nisan until the end of the fifth hour, just before we burn what’s left at the start of the sixth. Rabbi Yehuda, however, permits eating only through the fourth hour and has us wait an hour before we burn what’s left at the start of the sixth.
To understand the logic undergirding this argument, the Gemara brings another teaching from Sanhedrin:
If one says the incident occurred at the second hour of the day and one says it happened at the third hour, their testimony is valid. However, if one says it occurred at the third hour and one says it took place at the fifth, their testimony is void. This is the statement of Rabbi Meir.
Rabbi Yehuda says: In the last case, their testimony is valid.
Here, as in our mishnah on burning hametz, there is a disagreement between Rabbi Meir and Rabbi Yehuda. Rabbi Meir rules that a discrepancy of one hour does not invalidate the testimony of two witnesses, but that a discrepancy of two hours does. Rabbi Yehuda, however, accepts testimony that contains a discrepancy of two hours.
How does this relate to our mishnah? Abaye explains:
You will find that you can say that according to the statement of Rabbi Meir a person does not err at all. According to the statement of Rabbi Yehuda a person errs up to half an hour.
Abaye explains that Rabbi Meir understands people to be very aware of time, so much so that their testimony that an event happened at a particular hour can be assumed to be fairly accurate. Rabbi Yehuda, however, believes that a person’s estimation of time can be less accurate; thus a discrepancy of one half hour (in each direction) is within the margin of error and is acceptable testimony.
Similarly, when it comes time to stop eating and start burning hametz, Rabbi Yehuda builds in a margin of error. Believing that people have a rougher sense of time, he asks us to stop eating leaven during the fourth hour, set it aside for the fifth and burn at the beginning of the sixth — using the fifth hour as a buffer in order to be certain that we do not accidentally keep eating the leaven into the sixth hour. Rabbi Meir, however, believes that people keep track of time accurately and do not require this extra hour; he allows people to eat right up until the moment of burning.
The text from Sanhedrin brings to light underlying assumptions which are at the heart of the debate between Rabbi Meir and Rabbi Yehuda. If the Gemara had not juxtaposed these two texts, we may not have fully understood the difference of opinion in our case.