Rambam - 1 Chapter a Day

As we explained, every entity, whether a person or a k'li, that contracts impurity from a primary source of impurity is considered as a primary derivative of impurity until immersion in a mikveh. After immersion, he or it is considered like a secondary derivative of impurity until nightfall, as implied by Leviticus 11:32: "It shall be inserted into water and it will be impure until evening, when it will become pure." Thus Scripture refers to an entity immersed that day as impure.

The same status applies both to one who immersed to purify himself from severe impurity, e.g., that of a zav, that connected with a human corpse, or tzara'at, and one who immersed to purify himself from the impurity stemming from the carcass of a teeming animal and the like. Any entity, whether a person or a k'li, that must wait until nightfall to regain purity, regardless of whether the impurity stems from Scriptural Law or the words of the Rabbis, is considered as a secondary derivative until nightfall.

Contact with a person who immersed himself that day disqualifies foods that are terumah, liquids that are terumah, sacrificial foods, and consecrated liquids. It disqualifies everything.

What is implied? If a person who immersed that day touches food that is terumah, he causes it to be considered a tertiary derivative of impurity, for he is a secondary derivative. Similarly, if he touches liquids that are terumah, he imparts impurity to them and they are considered tertiary derivatives of impurity. In the same vein, if such a person touches consecrated liquids, he imparts impurity to them and they are a fourth degree derivative of impurity. Similarly, if he touches consecrated food, he causes them to be considered a fourth degree derivative of impurity. If, however, he touches ordinary foods or ordinary liquids, they remain pure. The laws that apply to those who are lacking atonement and one who immersed himself are the same with regard to touching consecrated food.

From this entire discussion, one has learnt that liquids are never considered a secondary derivative. They are always considered as primary derivatives with the exception of liquids touched by a person who immersed himself that day which are considered as tertiary derivatives if they were terumah or a fourth degree derivative if they are consecrated foods.

Fluids, e.g., saliva or urine, produced by any of those who impart impurity - whether severe or light - are governed by the same laws as the liquids that they touch. They are all primary derivatives of impurity, as we explained, with the exception of those produced or touched by a zav and those like him. The fluids such individuals produce are primary sources of impurity, while the liquids they touch are primary derivatives of impurity. Even when a person contracts impurity by eating impure foods or drinking impure liquids, the fluids he produces are governed by the same laws as the liquids he touches, i.e., they are primary derivatives.

Similarly, the fluids produced by a person who immersed and is waiting for nightfall are governed by the same laws as the liquids he touches; they do not impart impurity to other entities at all. Instead, if such fluids touch ordinary liquids, they are pure. If they touch liquids that are terumah, they become tertiary derivatives of impurity. And if they touch consecrated liquids, they become fourth degree derivatives.

From the above, it should be clear that a tertiary derivative that is terumah or a fourth degree derivative that is consecrated does not impart impurity to other liquids or other foods. Needless to say, it does not impart impurity to keilim.

Therefore, the following rules apply when there was a pot full of liquids and a person who had immersed that day touches it. If they were ordinary liquids, everything is pure. If the liquids were terumah, the liquids are disqualified, but the pot is pure. If only the person's hands were impure, the liquids are impure, whether they are terumah or ordinary liquids. This is a stringency observed with regard to impure hands that does not apply to a person who immersed that day.

There is a stringency observed with regard to a person who immersed that day that does not apply to impure hands: If there is a question regarding the status of a person who immersed that day, he disqualifies foods and liquids he touches because of that question. If, by contrast, the status of a person's hands is in doubt, the entities he touches are pure, as will be explained.

Both a person who was pure, but his hands contracted impurity and a person who immersed that day whose hands contracted impurity, impart impurity to ordinary liquids to cause them to be considered as primary derivatives of impurity that impart impurity to foods and liquids, as we explained.

Since the fluids discharged by a person who immersed that day are governed by the same laws as the liquids he touches, if the saliva or the urine of a person who immersed that day falls on a loaf of bread that is terumah, it is pure, because the fluids are like the liquids that he touches.

From all the concepts that we have stated previously, it is possible to comprehend that a person may become a source of impurity and he may be a primary derivative of impurity according to Scriptural Law. A person will be considered as a secondary derivative only according to Rabbinic Law. This refers to one who partakes of impure foods or drinks impure beverages or one who inserts his head and the majority of his body into drawn water. In all of these instances, the person is a secondary derivative of impurity according to Rabbinic Law.

Similarly, all types of keilim with the exception of earthenware containers can become primary sources of impurity or primary derivatives of impurity according to Scriptural Law. A k'li will be considered as a secondary derivative only according to Rabbinic Law; i.e., if it contracted impurity from impure liquids, it will be a secondary derivative according to Rabbinic Law, as we explained.

We already explained, that an earthenware container will never become a primary source of impurity, neither according to Scriptural Law, nor according to Rabbinic Law. It may become a primary derivative of impurity according to Scriptural Law and a secondary derivative according to Rabbinic Law if it contracted impurity from liquids, like other keilim. Neither persons, nor keilim ever become a third degree or a fourth degree derivative of impurity, neither according to Scriptural Law, nor according to Rabbinic Law.

Foods will never become a primary source of impurity, neither according to Scriptural Law, nor according to Rabbinic Law. They may become primary and secondary derivatives of impurity according to Scriptural Law. For if a person or k'li that is a primary derivative of impurity touches food, it causes it to be considered a secondary derivative.

According to the Sages alone, foods may become third degree derivatives or fourth degree derivatives.

Liquids, e.g., the water on which the ashes of the red heifer have been sprinkled or the saliva or urine of a zav, may become primary sources of impurity according to Scriptural Law. And they may become primary derivatives of impurity according to Scriptural Law, e.g., if they touched a primary source of impurity. Similarly, if liquids touched a derivative of impurity - whether a person or a k'li - they contract impurity according to Scriptural Law and are considered as primary derivatives to impart impurity to other entities according to Rabbinic decree. Similarly, if liquids touched a secondary derivative of impurity - whether a person, a k'li, or foods, they are considered as primary derivatives to impart impurity to other entities according to Rabbinic decree, as we explained.

Similarly, liquids can become third degree derivatives or fourth degree derivatives according to Rabbinic decree. What is implied? If a person who immersed that day touches a liquid that is terumah, he causes it to be considered a third degree derivative. If he touches a consecrated liquid, he causes it to be considered a fourth degree derivative. There is no concept of a liquid being considered as a secondary derivative or indeed, anything other than a primary derivative except liquids touched by or fluids discharged by a person who immersed that day or one who is lacking atonement with regard to consecrated liquids, in which instance, he disqualifies them, but does not make them impure, as we explained.