Last week we learned the machlokes between Ran and Rabeinu Tam whether toch k'dei dibur is a din d'oraysa or a din derabannan to allow a buyer to say hello to his rebbe and resume negotiations in a business deal. The Rishonim and Achronim note that a number of gemaras do not seem to fit Rabeinu Tam's theory:
1. The gemara (Nazir 20) notes that if someone accepts a vow of nezirus and a friend declares tok"d the words "v'ani", "I too", even though these words alone would not consititute a valid kabbalas nezirus, in the context of tok"d their meaning is clear and the nezirus is binding. The Chasam Sofer (Shu"T E"Z #97) asks: if tok"d is just a takanah derabbanan, wouldn't the korbanos brought by this second nazir be chulin b'azarah on a d'oraysa level?
2. The gemara (Nedarim 87) implies that if a man does hafarah on his wife's neder but then discovers tok"d that it was really his daughter who took the neder, the hafarah is valid and does not need to be repeated. Ran (Nedarim 87) asks: if tok"d is a takanah, how on a d'oraysa level has the neder of the daughter been absolved?
3. The same sugya records that a person who tears kriya upon hearing of the death of a parent and then discovers tok"d that it was his child, and not his parent, who passed away, need not tear kriya again. How does a takanah derabbanan designed to protect a buyer/seller in business dealings relate to this scenario? Rabeinu Tam's position seems to relate only to verbal transactions, not to an activity like kriya.
4. Testimony requires two witnesses to appear together. The Mishna tells us that two individuals who testify within a span of tok"d of each other are considered one witness-group. If tok"d is only a takanah derabbanan, how m'doraysa can two individuals ever joined to form a witness pair?
The Divrei Yechezkel (#27) suggests that there are two seperate dinim which are derived from the principle of tok"d: 1) a delay of tok"d does not consititute a hefsek between two statements; 2) a statement may be retracted tok"d of being said. Rabeinu Tam agrees with the Ran that the principle of tok"d not constituting a hefsek is a din d'oraysa, which explains all the cases cited above. The diagreement between Rabeinu Tam and the Ran is with regards to the second aspect of tok"d. The Ran saw both of these rules as stemming from the same don d'oraysa, while Rabeinu Tam opined that the possibility of complete retraction tok"d was a takanah.
What the Divrei Yechezek does not explain (l'fi aniyus da'ati) very clearly is the basis for the Ran and R"T's disagreement over this point. The Rogatchover writes that dinim can be broken down into the poel, the peulah, and the nifal -- roughly meaning there is an actor, an event or occurance, and an effect that is produced. I believe the issue of tok"d can best be explained using this chakira. Does tok"d teach that a speaker is still engaged in talking until a break of greater than tok"d has occurred, or is the speaker considered done after a pause, but the effect of his words is delayed by the span of tok"d? If the speaker is still considered engaged in speaking so long as tok"d has not passed, then the Ran would seem to be correct in allowing for retraction. So long as a person has not finished a deal, then changes may be made. However, if the speaker is considered to have finished but the nifal effect is incomplete until tok"d passes, then Rabeinu Tam has a basis for his sevara. Considering whether events are simultaneous, e.g. was kriya simultaneous with news of death, was the father aware of his daughter's neder when his hafarah took place, etc. is a measure of the timing of the nifal effect (kriya, hafarah) relative to its cause. Rescinding an agreement involves more than that. Even if the nifal effect of an agreement is not considered set until three seconds after the speaker has concluded, what right does a speaker have (once his original activity of speech has ended) to rescind that agreement or block that effect from occurring? That necessitates a new takanah.