English Explanation of Mishnah Eduyot 6:2

Rabbi Joshua and Rabbi Nehunia ben Elinathan, a man of Kefar Habavli, testified concerning a limb [separated] from a corpse that it is impure;
whereas Rabbi Eliezer says: they declared [this] only of a limb from a living [man].
They said to him: is not there an inference from the minor to the major (kal: If in the case of a living man [who is himself pure] a limb severed from him is impure, how much more in the case of a corpse [which is itself impure] should a limb severed from it be impure!
He said to them: they have [nevertheless] declared it only of a limb from a living man.
Another answer: The impurity of living men is greater than the impurity of corpses, because a living man causes that on which he lies and sits to become capable of making impure a man and clothing, and [he causes also] what is over him to transfer impurity to foods and liquids- which is defilement that a corpse does not cause.
This mishnah contains Rabbi Joshua and Rabbi Nehunia ben Elinathan’s testimony regarding the impurity of a limb separated from a corpse.
The dispute in our mishnah concerns whether or not a limb separated from corpse transmits tent impurity (anything which is under the same roof with it becomes impure). Rabbi Joshua and Rabbi Nehunia state that it is impure. Rabbi Eliezer states that it is pure, and that the only type of “separated limb” which is impure is one that has been separated from a living body.
Rabbi Joshua and Rabbi Nehunya respond with a classic type of Talmudic argumentation, called a “kal vehomer”. Generally a corpse is considered the greatest source of impurity, whereas a living body is often not a source of impurity at all. [It is not in and of itself impure; it only becomes impure if it contracts it somehow.] If a limb separated from a living body is impure, even though the living body itself is pure, all the more so a limb separated from a corpse is impure, since the corpse itself is impure.
Rabbi Eliezer’s response is very typical of Rabbi Eliezer. He states that although Rabbi Joshua and Rabbi Nehunya’s reasoning may be good reasoning, the tradition that he received from his teachers was only that a limb separated from a living body was impure. Even though there may be logic in extending this principle to include limbs from corpses, Rabbi Eliezer does not believe that it is the sage’s responsibility to add on to received traditions. Rabbi Eliezer is known as an arch-traditionalist; in another place he claims never to have stated anything that he did not hear from his teachers. Here we see classic example of Rabbi Eliezer sticking to his received tradition, in the face of a good argument to extend that tradition.
The final section of the mishnah contains a logical refutation of Rabbi Joshua and Rabbi Nehunya’s kal vehomer argument. In order to refute a kal vehomer argument one must point out that one side is not always more stringent than the other side. In other words, if the kal vehomer was based on a stable, predictable relationship between two things, the refutation points out that this relationship is not so predictable. In this case Rabbi Joshua and Rabbi Nehunya had pointed out that a corpse is more impure than a living body, and therefore if something that comes from a living body is impure, all the more so the same thing that comes from a corpse will be impure. The refutation points out that with regards to some laws, the living body is a greater source of impurity than the corpse. A zav (a person with an unusual genital discharge) causes anything on which he sits or lies to become impure and able to transmit impurity to people or clothing. He also causes anything above him to become impure and able to transmit impurity to food and liquids. The corpse does not have such a strong ability to impart impurity. Since in some ways the living body can have a stronger impurity than the corpse, one cannot make the kal vehomer argument that Rabbi Joshua and Rabbi Nehunya tried to make.