פירוש על נגעים 5:5

שניהם טמאים – since it spread in both of them.

Introduction Today's mishnah clarifies when cases of doubt are deemed unclean.

אף על פי שחזרו להיות כסלע – for now one of them is ritually pure, but since they were obliged to regard themselves/obligate themselves for defilement, both of them are impure, as it is written (Leviticus 13:23): “[But if the discoloration remains stationary, not having spread, it is the scar of the inflammation] the priest shall declare him pure”/"וטהרו הכהן" - that which is definitive, he (i.e., the Kohen) declares pure, but he does not declare pure the doubtful (see also Sifra on his verse in Leviticus).

"But after uncleanness has been established a doubt is regarded as unclean." This is a quote from mishnah four.

עד שיחזרו להיות גריס – that now, certainly both of them are ritually pure, that the spreading that on whose account they were declared to be certified lepers has disappeared from both of them.

How so? If two men came to a priest, one having a bright spot of the size of a split bean and the other having one of the size of a sela and at the end of the week each was of the size of a sela and a little more, both are unclean; The difference between this mishnah and yesterday's mishnah is that in this case, both negaim spread. One began at the size of a split bean and spread to be a bit larger than a sela, and one started as a sela and spread just a little bit. Nevertheless, since both spread both are impure.

And even though both returned to be the size of a sela both are unclean, and remain unclean until they return to the size of a split split bean. They remain impure even if both return to be the size of a sela. This is the "doubt." One of these has returned to its original size, and since the "spreading" is gone, that one should be pure. But since they were already pronounced unclean, they both remain impure until the spreading has certainly disappeared from both.

They is what they meant when they said, "but after uncleanness has been established a doubt is regarded as unclean." A summary of what was taught above.