A significant portion of Masechet Keilim deals with the purity and impurity of an oven and stove made of cheres (earthenware). The Bartenura explains that the oven was a kli that was open at the bottom; the ground served as its bottom. Therefore the fact that it can receive tumah is a chiddush (novelty) because clay utensils ordinarily must have a beit kibul (receptacle) to be susceptible to tumah. The Bartenura explains that the oven is different as its tumah is due to a gezeirat ha’katuv (decree of the Torah).
The Tifferet Yisrael explains that there is a greater chiddush that can be learnt from the fact that an oven receives tumah. There is a general rule that anything which is attached to the ground cannot receive tumah. Most of the ovens used at that time were attached with clay to the ground. Therefore, one would think that these keilim would not be susceptible to tumah. However, the gezeirat ha’katuv comes to teach us that these types of ovens, as well as portable ovens8 can receive tumah.
Interestingly, the Tosfot Yom Tov states that there were times that ovens were actually placed on a base (Bava Batra perek 2). This opinion would hold that there would be no need for the gezeirat ha’katuv as the oven would be tamei by virtue of it being a regular kli (with a beit kibul).
When discussing the different sizes of an oven the Mishnah (5:1) states:
An oven, its beginning (i.e. minimum size to be mekabel tumah) is four tefachim, and its remnant’s [minimum size] is four, so says R’ Meir. The Chachamim state “What is the case referring to? To a large oven. However, a small oven its beginning is kol she’hu [lit. anything – here, a tefach] and its remnant’s [minimum size] is the majority [of its original size]…
There are a number of explanations for the opinion of the Chachamim. Rashi and the Bartenura explain there are two different types of ovens. One is a large oven which is used to bake bread. The method of use for this oven is to take dough, and to stick it on the inside wall of the oven leaving it to bake. This type of oven must be at least four tefachim high to receive impurity. However, there is another type of oven, the small oven, which can be any size and receive impurity. This type of oven is one which is made as a toy for children to play with. Therefore, Rashi says the differentiation between large and small is solely based on the function of the oven.
The Tosfot challenge this interpretation. They ask why a large oven which is less than four tefachim is deemed tahor, and yet a small oven of the same size can be tamei. How does the classification of the oven as small or large, whether it is used as an oven or a toy, make a difference to the status of its purity? They answer that it must be that the “large oven” is significantly different in its properties to the small oven, in its height, width or thickness of the walls. The physical differences between these two utensils lead to the differences in shiurim for tumah.
This argument provides further insight into the Gemara in Niddah (26b). There the Gemara discusses a “Tanur Banot Tefach”. The explanation of this cryptic statement will be different depending on the views of Rashi and Tosfot. Rashi would hold that the oven of young girls (i.e. children) is a tefach in height. This follows his explanation here, that a small oven is one that is used as a children’s toy. However, Tosfot would explain that the words ‘banot’ and ‘tefach’ are joined words9. Therefore banot tefach is not referring to the fact that young girls use it as a toy, but rather solely a description of its height.
8 The Tifferet Yisrael quotes the Gemara (Shabbos 125a) which mentions certain types of portable ovens that Arabs used to take in to the desert loaded on the back of camels. If these ovens were open at the bottom like the other ovens of the time they would also be covered off by the gezeirat ha’katuv.
9 Other examples of joined words brought as examples by Tosfot include – ‘Ben Krach’ or ‘Ben Ir’.
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