Kelim, Chapter Thirteen, Mishnah Seven
This mishnah deals with vessels that are basically wooden, but have one part made of metal.
1) If Ashkelon grappling-irons were broken but their hooks remained, they remain susceptible to impurity.
2) If a pitch-fork, winnowing-fan, or rake, and the same applies to a hair-comb, lost one of its teeth and it was replaced by one of metal, it is susceptible to impurity.
3) And concerning all these Rabbi Joshua said: the scribes have here introduced a new principle of law, and I have no explanation to offer.
Section one: Since the hooks are the main parts of the grappling-irons, as long as they remain, the vessel is susceptible to impurity. Furthermore, although the vessel is made of wood, since its hooks are of metal, it is susceptible.
Section two: These are all tools with teeth. Most of the tool is made of wood, but one of the missing wooden teeth was replaced with metal. This one metal tooth gives the entire vessel the status of a metal vessel and it is therefore susceptible to impurity.
Section three: Rabbi Joshua adds here a fascinating note, one which I don’t believe we have encountered elsewhere in the Mishnah. In all of the above cases, since the basic vessel was of wood, and it was a simple vessel without a receptacle, the vessel should not have been susceptible to impurity. The innovation that the earlier scribes innovated was that although only one part was of metal, the entire vessel is susceptible.
Rabbi Joshua accepts this innovation, but nevertheless admits that he does not understand it. We can see here his deference to tradition, and yet his striving to understand it, and his sense of frustration when he cannot. This is an attitude that I believe is very typical among rabbis. They have a strong sense of respect for tradition, and yet they do not simply accept all that they have received. Rather, they constantly attempt to understand the early halakhot, to make sense out of them, and to use the principles that they perceive as underlying these halakhot to derive further halakhot.