Siman שט"ו
📑 Plan of the Synthesis
- The Central Axiom of the siman
- Key concepts condensed
- Hierarchy of cases — from broadest to most restrictive
- Decision tree
- Gag vs Mechitza — where the line of the ohel runs
- Pitfalls to avoid
- Modern practical cases
- Final synthesis table
- The practical commandments
1. The Central Axiom
Making an ohel (roof, shelter) on Shabbat = toldah of boneh, asur even when arai (temporary). But the issur falls only on the roof (gag) — the walls (mechitzot) are mutar. And if a tefach of roof was already there before Shabbat, one may complete it (tosefet ohel).
2. Key concepts condensed
| Concept | Definition | Application |
|---|---|---|
| אהל | Roof, shelter | Toldah of boneh |
| גג | The roof (horizontal plane) | The only thing the issur applies to |
| מחיצה | Vertical partition | Mutar — except when it "makes valid" |
| אהל קבע / עראי | Permanent / temporary shelter | Keva = d'Oraita; arai = d'Rabbanan |
| תוספת אהל | Addition to an existing shelter | Mutar if a tefach was pre-existing |
3. Hierarchy of cases
4. Decision tree
5. Gag vs Mechitza — where the line of the ohel runs
The entire siman hangs on one border: the issur of אהל hits the roof (גג), not the wall (מחיצה). To draw a curtain, set up a screen — mutar; to spread a horizontal cover over an empty space — asur. But this sharp split hides two borderline cases where it wavers, and that is where the real difficulty of the siman is decided.
Why the roof, not the wall
The essence of boneh, of which ohel is a toldah, is the sheltered and shaded space that one makes habitable. It is the horizontal plane that "covers": it is what creates the shelter. A wall alone, however tall, shelters from nothing as long as nothing crowns it — hence its principled heter. The practical rule flows from this: what one sets up vertically is free; what one stretches horizontally over a void of one tefach is the object of the issur.
First borderline case: the mechitza that "makes valid"
A mechitza ceases to be innocent when it does not merely separate but produces a constitutive halakhic effect: a wall that completes the validation of a sukkah, or that closes a space to permit carrying. There, raising the wall is equivalent to completing a structure — it has become an act of building, asur, even though it is a vertical plane.
Second borderline case: the pre-existing tefach
The roof itself is not absolutely locked. If a tefach of roof already existed before Shabbat, completing it is no longer "making an ohel" but only תוספת אהל — an addition to a shelter already born. Since the melakha is the creation of the shelter, an act that merely enlarges it escapes the issur.
6. Mnemonic "גמ"ת"
ג — Gag (גג) — the roof: asur to make.
מ — Mechitza (מחיצה) — wall: mutar.
ת — Tosefet (תוספת אהל) — completing a pre-existing tefach: mutar.
— The essence of the ohel is the roof that shades.
7. Pitfalls to avoid
8. Modern practical cases
| Situation | Practice |
|---|---|
| Opening an umbrella | Asur (ohel arai) |
| Umbrella already open before Shabbat | Mutar to stand under it |
| Stroller hood (tefach spread before Shabbat) | Mutar to complete (tosefet) |
| Curtain, screen, partition | Mutar (mechitza) |
| Crib mosquito net forming a roof | Set up before Shabbat |
| Covering a pot | Mutar |
| Retractable patio awning / blind | Tefach before Shabbat → completing mutar |
| Children's play tent | Set up before Shabbat |
9. Final synthesis table
| Element | Detail |
|---|---|
| Subject of the siman | The melakha of ohel — making a roof/shelter on Shabbat |
| Number of seifim | 13 |
| Mishna Berura | 49 entries |
| Talmudic source | Shabbat 137b-138a (ohel arai) |
| Melakha | אהל — toldah of בונה |
| Key distinction | גג (roof, asur) vs מחיצה (wall, mutar) |
| Practical pesak | Don't make a roof; spread a tefach before Shabbat; walls mutar |
10. The practical commandments of Siman שט"ו
Roofs and shelters on Shabbat — the checklist
- Don't make a roof on Shabbat (umbrella, tent, awning) — even temporary.
- Solution: spread a tefach before Shabbat → one can then complete (tosefet ohel).
- Vertical partitions (curtains, screens) = mutar.
- Mechitza that makes a sukkah valid / creates a reshut = asur.
- Umbrella: absolutely asur to open on Shabbat.
- Hood / mosquito net: prepare the structure before Shabbat.
- In case of safek → consult the Rav.
You have studied Siman שט"ו in 3 levels:
- 🌱 Level 1 — Base: the 13 seifim, translation, halakhic concepts
- ⚡ Level 2 — Lamdan: talmudic sources, shitot of the Rishonim, machlokot, nafka minot
- ✨ Level 3 — Synthesis: axiom, mnemonic, decision tree, practical commandments