We'll talk about a machloket (dispute) regarding utensils and whether they can become tameh (ritually impure). The Mishnah says there are four things that Rabban Gamliel says can become tameh because they are utensils. And Hachamim (the Sages) disagree and say that they will always remain tahor (pure).
Number one is the cover of a metal basket. These types of metal baskets were used to hold broken scrap metal. Rabban Gamliel says that these items are utensils, and the cover can become tameh because, if you hold it upside down, for example, it looks like a bowl. It looks like something could be held in it. So it is considered a utensil. Hachamim argue that people only use it as a cover. They cover the basket. So it is not an actual utensil, and it always remains pure. It cannot become tameh.
It is a rule of thumb that we have to remember throughout these Mishnayot: only something that has a use and could be a keli (utensil) is considered something that can become tameh.
Number two is the hook of a bathing comb. At the time, they would hang up all the combs they used to clean their skin. They would hang them on a certain type of nail in the bathhouse. According to Hachamim, this type of nail cannot become tameh, while Rabban Gamliel says it can because it has its own shape. It looks a certain way, and therefore it is a utensil in its own right and can become tameh.
Number three: there are metal utensils that are usable but are missing something. They have not yet reached the point of gemar melacha (completion of work). They are not engraved or polished. Rabban Gamliel says that, bottom line, they are usable, so they are considered utensils and can become tameh. But Hachamim say no: until they are finished, they are not considered utensils.
The last case is a tray that was split into two pieces that are the same size. According to Rabban Gamliel, both pieces can become tameh. Even though they look to be the same size, they cannot really be the same size: one is bigger than the other. The bigger piece can certainly become tameh because it is the majority of the original tray that broke. So, at this point, we do not know which one is bigger, and we have to treat both of them as if they can become tameh. But according to Hachamim, we assume that both pieces are the same size. Neither one is the majority of the original tray; each is only half of it. So neither one retains that original status, and neither can become tameh.
We will have a case where Hachamim agree that one of the pieces can become tameh, and we will add Hachamim to Rabban Gamliel. Hachamim agree with Rabban Gamliel. We have a tray that was split into two pieces: one was big and one was small. The large piece is tameh. It is capable of being a utensil and therefore can become tameh because it is the majority of the original tray. It retains that keli status. But the small piece is tahor. It cannot become tameh because it is only a small piece of the original tray. Therefore, it is not a continuation of what that tray was.