Throughout Tractate Eruvin, we have repeatedly encountered the measurement of four amot, a common talmudic unit of measure we generally translate as “cubits.” When you find yourself in a public domain without an eruv, you are allowed to carry objects only four cubits. Similarly, if you wander outside the standard 2,000-cubit radius that you are permitted to travel within on Shabbat, you can walk only an additional four cubits.
The source (and limit) of this ubiquitous measurement is explored on today’s daf.
According to the mishnah we’ve been discussing for several days now, a person who falls asleep on the side of the road on Friday afternoon may only walk on Shabbat four cubits from where they slept. Because they slept through sunset and did not officially declare that spot to be their place of residence, they are not permitted to move about in the normal 2,000 cubit range allowed on Shabbat. When they wake up, they are stuck in their four-cubit encampment.
Perhaps because of the severity of being stuck on the side of the road in a four-by-four cubit box, the Gemara inquires after the source of this measurement: Do we have to be this strict? Is it written somewhere in the Torah?
The Talmud teaches:
The verse “Remain every man in his place; let no man go out of his place on the seventh day” (Exodus 16:29), means one must restrict his movement to an area equal to his place. And how much is the area of his place? A person’s body typically measures three cubits, and an additional cubit is needed in order to allow him to spread out his hands and feet, this is the statement of Rabbi Meir. Rabbi Yehuda says: A person’s body measures three cubits, and an additional cubit is needed in order to allow him to pick up an object from under his feet and place it under his head, meaning, to give him room to maneuver.
In looking for the source of the four-cubit rule, the Talmud turns to a verse in Exodus, in which the Israelites are told they don’t need to go out to gather manna on Shabbat because they will receive a double portion of it on Friday. Generally, this verse is read to mean that the Israelites should just stay home on Shabbat. But a literal reading could be that you have to stay exactly within the space your body occupies for all of Shabbat. From this reading, the Gemara concludes that the area a person’s body occupies — which permits them to stretch out and get comfortable for sleep — is four cubits.
The Gemara asks: Are all people the same height and need the same amount of personal space? Does one size fit all?
The details of this case stirs a significant question about the standardization of the cubit itself. In Hebrew, an ammah is literally a forearm. The standard measure of a cubit is the length of an average man’s arm, measured from the elbow to the tip of the middle finger. But just as everyone has a different height, everyone’s ammah is different. And if you are confined to your personal space for all of Shabbat, how you measure four cubits matters a great deal.
The Talmud continues:
If he said to you that we provide him four cubits measured according to the standard cubit used for consecrated property, the standardized cubit, what will be with regard to Og, king of the Bashan, who is much larger than this?
If we go by a single objective standard of a cubit, then Og — the biblical giant who is a source of recurring fascination for the rabbis — would be pretty cramped. An extreme example, perhaps, but the point is clear: Bodies are very different, and a standard measure of four cubits would clearly cause problems for some people.
In the vast majority of cases, the four-cubit measure is a theoretical concept symbolizing personal space, not an accurate measure of the space needed to accommodate an actual body. Usually, having one standard measure of a cubit for all people isn’t a problem. In our case, this isn’t so — the measurement marks the actual space a person takes up when lying on the ground. Still, the rabbis prefer the standardized measure, even if that means some have more or less space to stretch out. Only in a few exceptional cases does the cubit revert to the subjective and individual measure of personal space.