Eruvin 14a

עירובין י״ד ע״א

Learn Eruvin 14a step by step: Aramaic beside English, every question, answer and proof colour-coded.

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Topic

The width, strength, and shape of the קורה over a מבוי, and the 3:1 circle ratio learned from שלמה's ים

Overview

The גמרא opens by asking how a קורה only one טפח wide can hold an אריח that is a טפח and a half wide. The answer is that plaster holds the extra half טפח in place. רבה בר רב הונא and רב חסדא then disagree about whether the beam's supports must also be sturdy. רב ששת rules that a beam covered by a mat hanging three טפחים off the ground counts as neither a קורה nor a מחיצה. A ברייתא follows with cases of beams that leave a gap, two thin beams side by side, and beams at different heights, along with the disputes of רבן שמעון בן גמליאל and רבי יוסי ברבי יהודה. רב corrects the משנה's wording to 'wide and sturdy' and explains that a beam four טפחים wide is a different case. The גמרא then explains why the משנה needed its lines about straw, curved, and round beams, including רבי זירא's rule for a curve that leaves the valid zone. Finally it proves from שלמה's ים that a circle three טפחים around is one טפח across, and begins working out the ים's volume, a discussion that continues on the next amud.

Opening lines

The steps (35)

1. ChallengeWhy only one handbreadth if the brick is wider?
2. ResolutionThe extra half handbreadth is held on with plaster
3. StatementOnly the beam must be sturdy, not its supports
4. StatementBoth the beam and its supports must be sturdy
5. StatementA beam covered by a mat raised three handbreadths works as nothing
6. StatementWhy it fails as a beam and as a partition
7. StatementA beam that does not reach across the alley
8. Statementרבן שמעון בן גמליאל allows a gap of up to four
9. StatementTwo thin beams placed side by side
10. Statementרבן שמעון בן גמליאל requires the brick's full length
11. StatementOne beam high and one beam low: picture them together
12. Statementאביי: the son agrees with his father about 'viewing as if'
13. Statementאביי: the son disagrees with his father about beams above twenty cubits
14. Statementרב יהודה teaches the משנה's line 'wide even if not sturdy'
15. Rejectionרב corrects the wording to 'wide and sturdy'
16. Challengeרב seems to contradict himself about sturdiness
17. ResolutionA four-handbreadth beam is a different kind of case
18. ChallengeWhy mention a straw beam at all?
19. ResolutionStraw teaches that רואין works even for a weak material
20. ChallengeA curved beam viewed as straight seems obvious
21. ResolutionThe curved-beam line teaches רבי זירא's rule
22. Statementרבי זירא's rule: mentally remove the part outside the valid zone
23. ChallengeIsn't רבי זירא's rule obvious too?
24. ResolutionThe case where the curve sticks out past the alley
25. ChallengeWhy does the משנה mention a round beam?
26. ResolutionThe real point is the measuring rule
27. QuestionWhere does the 3-to-1 rule come from?
28. Responseרבי יוחנן's source: the ים that שלמה built
29. ChallengeWhat about the thickness of the rim?
30. ResolutionThe rim was as thin as a lily petal
31. ChallengeEven a thin rim has some thickness
32. ResolutionThe circumference was measured from the inside
33. Statementרבי חייא: the ים held 150 מקואות
34. QuestionHow big is a מקוה?
35. ResponseA מקוה is 40 סאה, with a source