Ohalot, Chapter One, Mishnah Three
1) What is the case of four? Vessels touching a corpse, a person [touching these] vessels, and [other] vessels [touching this] person, are defiled with seven days’ defilement.
a) The fourth, whether a person or vessels, is defiled with a defilement [lasting until the] evening.
2) Rabbi Akiva said: I have a fifth, [if] a peg was fixed in a tent, the tent, the peg, a person touching the peg and vessels [touching] the person are defiled with seven days’ defilement.
a) The fifth, whether a person or vessels, is defiled with a defilement [lasting until the] evening.
b) They said to him: the tent does not count.
Section one: When vessels come into contact with a corpse, they are defiled for seven days (as in yesterday’s mishnah). If a person touches these vessels, he is impure for seven days, for they also are a “father of impurity.” And the person too is a “father of impurity” and if other vessels touch him, they are impure for seven days.
Section two: However, when it comes to the fourth in the chain, the level of impurity is reduced. So if a person or a vessel has contact with the aforementioned vessel, he or it is impure only until the evening.
Section three: Rabbi Akiva is getting ambitious! He wants to find a series with five elements. A peg is fixed into the ground next to a tent but it is not part of the tent and there is a corpse in the tent. According to Rabbi Akiva, the peg and the tent count as two separate items. The tent overshadows the peg causing it to be impure and Rabbi Akiva counts it like a vessel that overshadows a dead body or touches it. The person who touches the peg is impure and becomes a father of impurity. Any vessels that touch the person are all impure with seven day’s impurity. That’s four. The person or vessel that touches the aforementioned vessels is impure but only until the evening.
The other sages respond that the tent itself does not count. Both the tent and the peg are impure for they are considered to have shadowed over the corpse, and the peg is not impure because of the tent. Therefore, we don’t begin the count from the tent, but rather from the peg, in which case there are only four, not five, in this chain.