When a revi'it of blood comes from two corpses, it is pure. To impart impurity, the entire revi'it must come from one corpse. When a backbone was put together from two corpses, e.g., some of the vertebrae came from one corpse and others, from another, when a skull was put together from two corpses, or a fourth of a kab of bones came from two corpses or a limb came from two corpses: in all these instances, impurity is not imparted when one is under the same structure, only through touching and carrying, as is true with regard to other bones.
An olive-sized portion of flesh that comes from two corpses, an olive-sized portion of netzal that comes from two corpses, and two handfuls of rekev that come from two corpses when the laws of rekev apply to each one of them, can be combined. Similarly, a half of an olive-sized portion of flesh and a half an olive-sized portion of netzal can be combined with each other. All of the other sources of impurity stemming from a corpse are not combined with each other, because they are not of equal measures.
🔗 Multiple Corpses
Parts from two different corpses generally do not combine for ohel impurity — a revi'it of blood, a backbone, skull, quarter-kab bones, and a limb from two corpses only impart touch and carrying. However, flesh and netzal combine across corpses (half-olive of each), as does rekev — but only because their measures match. A limb from a living person from two people is pure even if combined.
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Dividing and Rejoining — Human vs. Natural Joining
When a bone the size of a barley-corn is divided into two, it imparts impurity when carried. Similarly, when a quarter of a kab of bones were crushed, although none of them are the size of a barley-corn, they impart impurity when one is under the same shelter as if they were not crushed.
When an olive-sized portion from a corpse was cut into small pieces, flattened, and pressed together, it imparts impurity when under the same shelter and when carried, but it does not impart impurity when one touches a portion of it, even when the pieces are joined together, because anything joined together by man is not considered as joined.
When the majority of the vertebrae were taken from a backbone, it does not impart impurity when under the same shelter, even through its form remains. If it is in the grave, even if it is broken and even if it is crushed, it imparts impurity when under the same shelter. The rationale is that the grave joins it together.
Whenever a substance that imparts impurity when under the same shelter was divided and then both portions are brought into a house, it is considered as joined together by the shelter and impurity is imparted by them because of it.
🧩 Joining Rules
A bone the size of a barley-corn split in two still imparts carrying impurity. An olive of flesh cut into pieces and rejoined by human hands does not combine for touch (only for ohel and carrying) — because human joining is not considered joining. Natural attachment ('by Heaven'), however, is valid. A crushed spine inside a grave is joined by the grave itself.
Whenever a substance that imparts impurity when under the same shelter was divided and then both portions are brought into a house, it is considered as joined together by the shelter and impurity is imparted by them because of it.
When there is an olive-sized portion of flesh that grew on a bone through the influence of heaven, and a portion of that bone was brought inside a house, the house contracts ritual impurity. If the flesh had been pushed into the bones by humans, the house is pure. The rationale is that anything joined by man is not considered as joined.
When a revi'it is absorbed in a house, in the future, the house is pure. Anything that was in the house at the time the blood was absorbed in the earth, is impure.
When an olive-sized portion of a corpse was lost inside a house and it was searched for and not found, the house is assumed to be pure. If it is discovered afterwards, the house is deemed impure retroactively from the time it was lost until the time it was discovered.
🏠 Ohel Combines
When multiple portions of impurity — each below the ohel minimum — are brought into a house, the ohel (house) joins them together, making the whole house impure. A bone with an olive of flesh grown naturally on it (not by human hand) makes the house impure when any part enters. Two handfuls of rekev spread through a house makes the house impure.
When an olive-sized portion of a corpse was lost inside a house and it was searched for and not found, the house is assumed to be pure. If it is discovered afterwards, the house is deemed impure retroactively from the time it was lost until the time it was discovered.
The following laws apply when a revi'it of blood was poured in an open space. If it coagulated or it was in a place where it could collect, i.e., a low place like a pit and an entity projects over even a portion of it, that entity is impure. If it was spilled on the doorstep which was on an incline, whether to the inside or outside, the house is pure. The rationale is that the blood did not come to rest on the doorstep. If the doorstep was a place where the blood could collect or it coagulated there, the house is impure. The following laws apply when a revi'it of blood is absorbed in a garment. If it could be washed and a revi'it of blood would be discharged from it, the garment imparts impurity when touched, carried, or when one is under the same shelter. If not, it does not impart impurity when one is under the same shelter and it is considered as a garment that came into contact with a corpse. The rationale is that whenever something absorbed cannot be discharged, it is considered as pure. How is the quantity of blood measured? The garment should be washed in water. Then an equal quantity of water should be brought and a revi'it of blood placed in it. If their appearance was the same or the water in which the garment was washed was of a redder hue than the mixture, it is apparent that a revi'it was discharged.
Carrying, touching, and being under the same structure are three different categories. Whenever activities come from one category, they can be combined and impart impurity. If they are from two categories, they are not combined and are pure. What is implied? A person becomes impure in all of the following situations, for the activities that are combined are from the same category: a) He touches two portions of a corpse that are half the size of an olive at the same time or carries two portions of a corpse that are half the size of an olive at the same time. b) He stands over two portions of a corpse that are half the size of an olive. c) He stands over a portion of a corpse that is half the size of an olive and has a similar portion hang over his body. d) He and a portion of a corpse half the size of an olive were under one shelter and a portion of his body stood over another similar portion, or a similar portion was suspended over his body. One is, by contrast, pure in all of the following situations. He touches a portion of a corpse half the size of an olive or carries such a portion and: a) another entity covers both him and another such portion from a corpse; b) another such portion was suspended over a portion of his body; c) he stood over such a portion, or d) he touched such a portion and carried such a portion. The rationale is that a quantity that is touched is not combined with one that is carried, neither with regard to a corpse, nor with regard to other forms of impurity. Similarly, a quantity that is touched is not combined with one that is governed by the laws of ohel, nor is one governed by the laws of ohel combined with one that is carried, because they are not from the same category.
הלכה ט״ו׳
🩸 Blood Scenarios
A revi'it of blood absorbed into the earth no longer imparts impurity going forward, but whatever was in the house at the moment of absorption is impure. Blood spilled in open space: if it coagulates or pools in a low place and one hangs over part of it, they become impure. Blood absorbed in a garment: if it can be washed out as a full revi'it, the garment is impure.
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🎓 Key Principles
Chapter 4
🔗
Natural vs. Human Joining Only naturally-grown flesh on bone constitutes a valid joining for ohel impurity — joining by human hands is legally ineffective.
🏠
The Ohel as Unifier A shared shelter (ohel) can join otherwise-insufficient portions of impurity, making everything inside impure collectively.
🩸
Blood Absorption Ends Impurity Once a revi'it of blood is absorbed into the ground, it ceases to impart future impurity — only things present at the moment of absorption are affected.
⚖️
Corpse Parts from Two Sources Don't Combine for Ohel Most corpse impurity sources require a single corpse to achieve their measure for ohel impurity — combining parts from two corpses only yields touch and carrying impurity.