All piggul [foods] combine with one another. All nossar [foods] combine with one another. All neveilos combine with one another. All shera- tzim combine with one another. The blood of a sheretz and its meat combine with each other.  R’ Yehoshua stated a general rule: All [items] whose tumah [transmission] and [minimum] measure are the same, combine with one another. [If] their tumah [transmission is the same] but not their [minimum] measure, [or if] their [minimum] measure [is the same] but not their tumah [transmission], [or if] neither their tumah [transmission] nor their [minimum] measure [are the same], they do not combine with one another.

Piggul and nossar do not combine with each other, because they are two [distinct] names. A sheretz and neveilah, as well as neveilah and flesh of a [human] corpse, do not combine with each other to transmit tumah even like the more-lenient [aspect] of the two. Food that contracted tumah from an av hatumah and [food] that contracted tumah from a vlad hatumah combine with each other to transmit tumah like the more-lenient [aspect] of the two.

All foods combine with one another: to disqualify one’s body with half a peras; for the food of two meals for an eruv [techumim]; for the egg’s volume to transmit the tumah of foods; for the dried fig’s volume for carrying out [of a domain] on the Sabbath; for the date’s volume on Yom Kippur.  All beverages combine with one another: to disqualify one’s body with a revi’is and for the “fill of a cheek” on Yom Kippur.

Orlah and kilayim of the vineyard combine with each other. R’ Shimon says: They do not combine.  Cloth and sack, sack and hide, hide and a mat, combine with one another. R’ Shimon says: Since they are fit to contract tumah as a seat.