Redeeming captive concepts in halachah
Last Shabbat, our rabbi led us in a group discussion about pidyon shevuim, the redemption of captives, and then related some basic information about the relevant mishnah, which I went and studied. The discussion in the Gemara is not as complicated as it is elsewhere, with the main considerations being the ability of the society to absorb the payment (dekhoka detsibura) and the fear that, sometime in the future (or in the present day) marauding bands of bandits will take Jews captive in order to ransom them (but see this mention of further complexities). There are various elaborations on these topics (Tosfos strive to reconcile the Mishnah with other episodes, where it seems that captives of special status can be redeemed for higher-than-normal sums; Rambam generalizes the marauding bands to "enemies"), but in the end the decision comes down to how like our situation is to the situation mentioned in the Mishnah.
This is the tricky part of halachic analogizing. Sometimes it's quite a stretch to find the source text which matches our present-day situation. Conversely, sometimes the governing principle seems clear to everyone (pidyon shivuyim was the halacha everyone readily referred to in the Gilad Schalit case), even though (a) he was not kidnapped by bandits, but by terrorists at war with an independent Jewish state; (b) the ransom paid for Schalit is possibly not a significant change from the past. With such dissimilarity one can ask if the original category applies.
You can always ask whether the concepts apply. This overlaps with a related question, whether halachah is (to use the common and frustrating term) "binding." If a halachic category is inapplicable to the present-day situation, no matter how God-fearing, or even intellectually respectful towards the halachic enterprise, we are, we can't possibly apply an inapplicable analogy. It would be like using a map of South America to navigate a college campus. More relevant than "binding," in such a case, would be the terms "useful" or "comparable."
Someone always needs to decide what is applicable. Don't swerve to the right or left – that's the Biblical verse which justifies rabbinical authority. But any rabbi which cannot justify his or her analogies is not someone whose psak we can follow. Analogies are made convincing by a number of strategies: either communal suasion/coercion or effective rhetoric. Psak is a lot like politics in this way. Thinking about it in this context, the catch-all of "siyata dishmaya" (Divine aid necessary for religiously "reliable" psak) is indeed necessary even to the modern mind: whatever makes an analogy convincing is just like whatever makes a novel speak to our heart. Who says the Divine isn't involved in that?
