Impurity does not enter a shelter, nor does it depart from it if there is an opening less than a handbreadth by a handbreadth. What is implied? When there is a window between one house and another or between a house and a loft, if it is a square handbreadth by a handbreadth and there was impurity in one of the structures, the other structure is also impure. If the window does not comprise a handbreadth by a handbreadth, impurity does not depart from it, nor does it enter the second structure. When does the above apply? With regard to a window made by a person for functional purposes. When, by contrast, a window was made by man for illumination, that light should enter, its measure is the size of pundiyon. Then ritual impurity departs through it. What is implied? There was impurity in a house. A person came and stood on the outside, near this window for light or placed a k'li there, or there was a covering on the other side of the wall, the person, the k'li, and everything under the covering to which the impurity passes through becomes impure. A window made for light is one that is not covered by a roof, but instead, is open to the sun.
When an aperture was not made through intentional human activity, e.g., it was hollowed out by water or crawling animals, the earth itself cratered, a window had been shuttered close and the shutter was removed, or it had been covered by glass and the glass broke, the minimum measure is the full span of a shingle which is the size of the head of an ordinary man. The above applies provided that the owner did not think of using that aperture for functional purposes. If, however, he thought of using it, the minimum measure is an opening of a handbreadth by a handbreadth. If he thought to use it for light, its measure is the size of a pundiyon. The rationale is that, in these instances, thought is considered equivalent to deed.
🪟 Window Reduction
A window can be reduced below the threshold by any substance the owner does NOT intend to remove. Rotting straw, rotted figs, or disgusting items with no value serve as valid reductions. Items the owner plans to move (non-rotted food, straw, growing grain) do NOT reduce a window. Grain that grew into a window does not reduce it — since one would remove it to prevent wall damage. But if it grew from a distance and bent into the opening — it does reduce.
When an aperture was not made through intentional human activity, e.g., it was hollowed out by water or crawling animals, the earth itself cratered, a window had been shuttered close and the shutter was removed, or it had been covered by glass and the glass broke, the minimum measure is the full span of a shingle which is the size of the head of an ordinary man. The above applies provided that the owner did not think of using that aperture for functional purposes. If, however, he thought of using it, the minimum measure is an opening of a handbreadth by a handbreadth. If he thought to use it for light, its measure is the size of a pundiyon. The rationale is that, in these instances, thought is considered equivalent to deed.
📋 Valid Reducers
Items that validly reduce a window: bitter grasses unfit for animals, rotting cloth patches (less than 3×3, too filthy for any use), bound gentile prisoner (cannot be released), eight-month infant on Shabbat (forbidden to move), salt mixed with thorns (on a shard so it won't damage wall), and a worn-out Torah scroll being permanently stored — all are not susceptible to impurity and the owner has no plan to move them.
The following rules apply when a person began closing a window opened for light and did not complete the task because he did not have sufficient cement or a colleague called him, night fell initiating the Sabbath, and there remained a small amount open. If a portion the height of two fingerbreadths and the width of a thumbbreadth remain, it conveys ritual impurity. If it is less than that, it is as if it was closed.
The following rules apply when there was a large window made for light covered by a lattice or the like. If there was one place where there is a hole as large as a pundiyon, it conveys ritual impurity and allows ritual impurity to depart. If the holes of the lattice are small and not one of them is the size of a pundiyon, it is considered as closed. Similarly, when there was a large window made for functional purposes and it was covered by thatchwork coverings or shades, if there was empty space a handbreadth by a handbreadth square, it conveys ritual impurity and allows ritual impurity to depart. Otherwise, it is considered as closed.
⚖️ Sub-Threshold Reducers
Less than an olive of corpse flesh, less than a barley-bone, less than a lentil of crawling animal, or less than an egg-sized food (not susceptible to impurity) — all can reduce a window since they are unimportant and the owner won't move them. However, they cannot reduce if they are the same type as the impurity inside — flesh cannot reduce a flesh-based window; a bone can reduce it (since it's a different type).
The following rules apply when there was a large window made for light covered by a lattice or the like. If there was one place where there is a hole as large as a pundiyon, it conveys ritual impurity and allows ritual impurity to depart. If the holes of the lattice are small and not one of them is the size of a pundiyon, it is considered as closed. Similarly, when there was a large window made for functional purposes and it was covered by thatchwork coverings or shades, if there was empty space a handbreadth by a handbreadth square, it conveys ritual impurity and allows ritual impurity to depart. Otherwise, it is considered as closed.
When a window is exposed to the open air, its minimum measure is the size of a pundiyon, because it is made solely for the purpose of light, as we explained. If one builds a house outside this window and thus the window is now under a roof, it is considered as if it is between two structures and its measure is a handbreadth by a handbreadth of empty space. If the roof was built in the middle of the window, the measure for the lower portion that is below the roof is a handbreadth by a handbreadth of empty space. The measure of the upper portion that is above the roof is the size of a pundiyon, because it is exposed to the open air.
🕸️ Special Cases
An earthenware vessel placed in a window with its opening facing out: since it does not contract impurity from its outer surface, it is pure and reduces the window — but it must be disgusting and perforated so the owner won't move it. Earth from a beit hapras made into a brick is pure (only a natural clod is impure) and can reduce a window. Spider webs reduce a window only if they have substantial physical mass.
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🎓 Key Principles
Chapter 14
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Abandonment Creates Valid Reductions The key criterion for window-reduction is whether the owner intends to remove the blocking substance — items that are rotting, disgusting, or permanently stored are considered abandoned and validly reduce openings.
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Beit HaPras Brick vs. Clod Earth from a beit hapras in its natural clod state is impure, but if formed into a brick it becomes pure — demonstrating that the Rabbinic decree applies only to the natural state of the earth.
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Same-Type Impurity Does Not Block Same-Type Impurity Less-than-minimum corpse flesh cannot block the threshold of a window protecting against corpse flesh inside — the same type of impurity cannot serve as a barrier against itself.
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Spider Webs Need Substance Spider webs can serve as a window reduction only if they have actual physical substance — mere gossamer threads without mass do not count.