Doesn’t the Torah say that a transgressor is whipped 40 times?How were the Rabbis allowed to reduce the number to 39?
Deut.25:2-3 says “he (an official) shall beat him (the transgressor) before him (the judge), according to his wickedness, a number [of times]; 40 shall he beat him, he shall not add (to it)”. It could have simply said “he shall beat him 40 times”, but it added the extra phrase “a number”. Based on this, the accepted opinion in the Mishnah (Makkos 3:10) is that the verse is referring to the number preceding 40, i.e. 39. (Deriving conclusions from extra words in verses is standard Midrashic practice. In this case, not everyone agreed with this interpretation of the verse; the Mishnah gives a second opinion, that of R.Yehudah, that transgressors were beaten 40 times, not 39, but the more lenient opinion was accepted.) If Deut.25:2-3 had said “he shall beat him 40 times”, leaving no room for any other interpretation, reducing the 40 to 39 would have been a violation of Deut.4:2 and 13:1; but in fact, we get the 39 by interpreting Deut.25 as meaning “up to but not including 40” rather than “exactly 40”. Thus 39 is an interpretation of the number in Deut.25:2-3, not a reduction of that number.