DAAT · LEVEL 3 — MASTER SYNTHESIS
Siman שס"ג
סימן שס"ג · דִּינֵי מָבוֹי וְלֶחִי
Recap & mnemonics for review
📑 Synthesis Plan
- The Central Axiom of the siman
- Key concepts condensed
- Hierarchy of concepts — from mechitzah to rope
- Decision tree — which tikkun?
- Lechi vs Korah — the comparative table
- Mnemonic לֶחִי
- Pitfalls to avoid
- Practical cases
- Final synthesis table
- Practical mitzvos
1. The Central Axiom
Siman שס"ג in one sentence.
A place closed by three mechitzos is reshus hayachid mide'oraisa; but since its fully open fourth side makes it resemble reshus harabbim, Chazal asur to carry there until a visible marker has been erected — a lechi (post), a korah (beam) or a tzuras hapesach (form of doorway). These tikkunim do not close anything: they signal that the place belongs to reshus hayachid.
A place closed by three mechitzos is reshus hayachid mide'oraisa; but since its fully open fourth side makes it resemble reshus harabbim, Chazal asur to carry there until a visible marker has been erected — a lechi (post), a korah (beam) or a tzuras hapesach (form of doorway). These tikkunim do not close anything: they signal that the place belongs to reshus hayachid.
2. Key concepts condensed
| Concept | Definition | Application |
|---|---|---|
| מָבוֹי | Alleyway with 3 mechitzos, open on one side | Validated by lechi or korah |
| לֶחִי | Post at the entrance, 10 tefachim high | No width measure — "kol shehu" |
| קוֹרָה | Transverse beam atop the entrance | Width of one tefach — prescribed measure |
| צוּרַת הַפֶּתַח | 2 posts + 1 crossbar | Opening > 10 amos, or chatzer status |
| פַּס | Partial wall segment (4 tefachim) | Validates a breached chatzer |
| לָבוּד | Gap < 3 tefachim deemed joined | Connects the lechi, closes gaps |
3. Hierarchy of concepts
Torah level: 3 mechitzos = reshus hayachid. No tikkun required mide'oraisa.
↓
Decree of Chazal: the open 4th side resembles reshus harabbim → carrying assur until a tikkun is in place.
↓
Mavoy: distant from reshus harabbim → light tikkun: a lechi OR a korah.
↓
Chatzer: more exposed → stronger tikkun: a pas of 4 tefachim.
↓
Wide opening (> 10 amos): only the tzuras hapesach works.
4. Decision tree
Q1: Does the place have 3 mechitzos and the 4th side open? (height ≥ 10 tefachim)
↓ YES
Q2: Is the opening less than 3 tefachim? → YES: deemed closed (lavud), nothing to do.
↓ NO (≥ 3 tefachim)
Q3: Does the opening exceed 10 amos? → YES: tzuras hapesach is required.
↓ NO (≤ 10 amos)
Q4: Is it a mavoy (2 inhabited chatzeros opening into it, length > width)? → YES: lechi or korah suffices. → NO: chatzer status, pas of 4 or tzuras hapesach.
↓
→ For the kashrus of a real eruv → rely on the Rav in charge of it.
5. Lechi vs Korah — the comparative table
| Criterion | Lechi (post) | Korah (beam) |
|---|---|---|
| Position | Vertical, at the entrance, against a wall | Horizontal, atop the entrance |
| Measure | No width prescribed ("kol shehu"); 10 tefachim high | Width of one tefach, strong for a half-brick |
| Asherah wood | Valid (no shiur to "grind") | Pasul — כתותי מכתת שיעורא |
| Mavoy height > 20 amos | Valid | Pasul (unless ornament/drawing) |
| Intent required | A fortuitous post suffices (if relied upon from erev Shabbos) | Must be placed to permit the mavoy |
6. Mnemonic לֶחִי
ל — לֶחִי כָּל שֶׁהוּא: the lechi has no width measure — any material, even debris, works; 10 tefachim high.
ח — חִיבּוּר וְהֶכֵּר: it must be stable (not toppled by the wind) and attached to the wall — less than 3 tefachim gap (lavud) — and recognizable as a lechi.
י — יֶתֶר עַל עֶשֶׂר — צוּרַת הַפֶּתַח: beyond 10 amos of opening, the lechi no longer suffices; a tzuras hapesach is needed.
7. Pitfalls to avoid
Pitfall 1: Thinking that the lechi or korah physically "close" the mavoy. They are markers; they lift a rabbinic isur, they do not create a physical mechitzah.
Pitfall 2: Applying to a chatzer the lighter regime of the mavoy. A chatzer requires a pas of 4 tefachim; only a chatzer longer than wide receives mavoy status (seif כז).
Pitfall 3: Confusing lechi and korah regarding asherah wood. The lechi remains valid; the korah, which has a prescribed measure, is invalidated.
Pitfall 4: For the tzuras hapesach, passing the wire on the side of the posts. The crossbar must pass above the posts (seif יד — the korah on the wall, not on outside pegs).
8. Practical cases
| Situation | Analysis | Conduct |
|---|---|---|
| Neighborhood eruv | Chatzer status (Rema, seif כו) | Tzuras hapesach: posts + wire |
| Narrow mavoy (< 3 tefachim opening) | Deemed closed by lavud | No tikkun needed (seif כח) |
| Steeply sloped mavoy | The slope counts as a mechitzah (seif לו) | No tikkun |
| Mavoy 20 amos wide | Too wide for a lechi alone | Central pas of 4 amos or lateral pasim |
9. Final synthesis table
| Element | Detail |
|---|---|
| Topic of the siman | The mavoy and its tikkun: lechi, korah, tzuras hapesach |
| Number of seifim | 36 (Mechaber's codification) |
| Mishnah Berurah | 157 entries |
| Talmudic source | Maseches Eruvin, perek kama |
| Golden rule | 3 mechitzos = reshus hayachid mide'oraisa; the 4th side requires a visible marker (Chazal's decree) |
| Practical decision | Rely on the Rav responsible for the eruv; Chabad — Shulchan Aruch HaRav siman שס"ג |
10. Practical mitzvos of Siman שס"ג
For daily conduct
- Three mechitzos make a reshus hayachid mide'oraisa; the open fourth side requires a rabbinic tikkun.
- Mavoy → lechi or korah; chatzer → pas of 4 tefachim; wide opening → tzuras hapesach.
- The lechi must be stable and recognizable; the korah must measure one tefach and be placed to permit the mavoy.
- Lavud (less than 3 tefachim) resolves position gaps for the lechi and korah.
- The urban eruv of our era rests on the tzuras hapesach (Rema's gloss, seif כו).
- For the kashrus of an eruv — rely on the Rav in charge; Shitah of the Alter Rebbe — Level 4.
📚 Recap of the study journey
You have studied Siman שס"ג in 3 levels:
You have studied Siman שס"ג in 3 levels:
- 🌱 Level 1 — Base: the 36 seifim, English translation, halachic concepts
- ⚡ Level 2 — Lamdan: talmudic sources, שיטות of the Rishonim, מחלוקות, נפקא מינות
- ✨ Level 3 — Synthesis: axiom, mnemonic, decision tree, practical mitzvos