SOME PROBLEMS IN THE RABBINIC USE OF THE QAL VA-CHOMER ARGUMENT

The qal va-chomer (a fortiori) argument is a logic of analogy, not of classes or sets (the subject-matter of Aristotelian logic), and this makes it suitable for legal, rather than scientific, argument. What makes it an exact reasoning is a special rule (unknown to Greek rhetorical use of a fortiori), namely the rule of dayyo, which lays down that the conclusion must not contain anything that was not present in the premises. For example: If a moderately good child deserves one sweet, a very good child all the more so deserves one sweet (correct); deserves two sweets (incorrect). Nevertheless, a qal va-chomer argument is not as unchallengeable as a syllogism, and the rabbis recognised various grounds of challengeablity. Especially interesting in this respect is the disagreement between the Sages and Rabbi Tarfon in Mishnah Bava Qamma 2:5. Is the qal va-chomer argument entirely logical, or does it contain an aspect of intuition? Can an argument be challengeable, yet rational? Is challengeability indeed a positive advantage in the search for rationality? This paper takes into account the view of the dayyo principle expressed in the Talmudic (Amoraic) discussion of b. Bava Qamma 25a, which makes it appear an arbitrary rule, rather than a principle of reasoning. This view is characterized as a falling-away from the more rational standpoint of the Mishnah. Also discussed is the relatively relaxed application of the rule of dayyo in aggadic discourse. An apparently flagrant breach of the rule in Mishnah Makkot 3:15, going far beyond the leniency of even aggadic discourse, is argued to be due to a mistranslation.