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Chapter 3, Mishna 7, 8

Looking at doubtful eruv for the purpose of shifting our Shabbos boundary (how far we can walk away from my dwelling on Shabbos) so we can better fulfill the commandment to delight in Shabbos. Question hinges on the nature of the doubt and when it took hold.

Was it ever a certain eruv, or was it doubtful from the start? If it became disqualified later, do we have reason to believe it became disqualified before Shabbos began?

To help us understand the nature of the doubt and how to resolve it, we look at related case of a tamei, ritually impure, person who immersed in a mikveh, ritual bath, in order to become tahor, ritually pure, only to learn later that the mikveh may not have been kosher.

And the case of one who touched another person in the night and woke up to discover that person is dead. Did he touch a living person – no impact – or a corpse, in which case he now has the severe ritual impurity of corpse tumah? Answer depends on which status quo we extend: that of the known tumah in the corpse, or that of the person who went to bed last night still alive.

Another case: one declares his eruv based on two loaves of teruma, consecrated food for a priest, one of which is known to be tamei and thus disqualified, but he is not sure which loaf.

Mishna 8 – One may make two conditional eruvs on Friday based on which direction he may have to travel on Saturday, either away from a corrupt tax collector or toward a Sage who’s giving a Torah lecture.