פירוש על טהרות 1:5

מצטרפין זה עם זה לטמא – if there isn’t in one of them the equivalent of an egg’s bulk, they combine to the measurement to defile according to the lighter/lenient of the two of them, for if it came in contact with/touched heave-offering, it invalidated it, according to the law of food that was defiled by the offspring of uncleanness that invalidates the heave-offering but does not defile it.

Introduction Today's mishnah deals with food that has become unclean and how much of it needs to be gathered together to convey uncleanness.

כחצי ביצה וכו' – that they mixed this one with that one.

Food that contracted uncleanness from a "father of uncleanness" and one that contracted uncleanness from a derived uncleanness may be combined together to convey uncleanness according to the lighter grade of the two. Food that has become unclean by contact with a "father of uncleanness" such as a sheretz, has first degree impurity. If it had contact with derived uncleanness, then it has second degree impurity. The mishnah now will illustrate how 1/2 of an egg's worth of food with one level of impurity can combine with another half of an egg's worth of food with another level of impurity to create the requisite amount to convey impurity.

שני – this mixture/combination has the law of second degree [of ritual impurity] upon it and it invalidates the heave-offering.

How so? If the amount of half an egg of food that has first grade uncleanness and the amount of half an egg of food that has second grade uncleanness were mixed together, the two are regarded having second grade uncleanness. The two half eggs that are mixed are considered only to have second degree impurity. This is the lighter form of impurity. If this piece of food comes into contact with terumah it will render the terumah invalid.

שלישי – and invalidates the Holy Things.

And if the amount of half of an egg of food that has second grade uncleanness and the amount of half an egg of food that has third grade uncleanness were mixed together, the two are regarded as having third grade of uncleanness. The piece of food with third degree uncleanness will render sacred things (such as sacrifices) invalid, but it will not disqualify terumah.

ראשון – and makes [through] its contact, second-degree [of ritual impurity]. For there is a measurement that first-degree [of ritual impurity] on the body to grant defilement.

If the amount of an egg of food having first grade uncleanness and the amount of an egg of food having second grade uncleanness were mixed together, both are regarded as having first grade uncleanness; But if they were then divided, each part is regarded as having second grade uncleanness. If each part separately fell on a loaf of terumah, they cause it to become unfit. But if the two fell together they cause it to have second grade uncleanness. In this case, both pieces of food are the size of an egg. Here, both are treated more stringently, as if both have first degree uncleanness. If after they were mixed together he separated them, then both are treated as if they have only second degree uncleanness, because both pieces now have less than an egg's worth of the original piece that had first degree uncleanness. If each of these pieces now falls separately on a piece of terumah, both are treated as if they have second degree impurity and they render the terumah invalid. They do not, however, cause it to be impure. However, if they both fall on one piece of terumah, then we know that an egg's worth of food that has first degree impurity fell on the terumah and the terumah now has second degree impurity.

חלקן זה שני וזה שני – for in each of them is half of the measurement of the first, and half the measurement of the second. And it is taught in the Mishnah above (see this Mishnah, Tractate Taharot, Chapter 1, Mishnah 5) that first-degree [of ritual impurity] and second-degree [of ritual impurity] combine to the lighter of the two of them.