Hazal Vs. Science Redux

In the near future I’m planning to post regarding several halakhic statements in Talmud which do not conform with the reality known today. As a preface to these posts I decided to rehash the basic opinions of the Hazal  versus science debate. I do not take any position in this post, as this is only intended to be an overview of the various positions on this matter.

One of the most famous scientific discrepancies found in Talmud is that of the sweat-louse. The Gemara states in BT Shabbat 107b that one may kill a louse in Shabbat, since lice do not reproduce sexually. Since this is one of the most popular Hazal vs. science case, I chose this as the prototype of the Hazal vs. science debate.

All was well, until the world discovered in the 19^th century that there is no such thing as spontaneous generation, and lice actually do sexually reproduce.

Two questions arose: First, how do we deal with this statement in Talmud? Can it be that they erred in science? If the Torah is God-given, how can there be mistakes in it? The second question is: what are the halakhic ramifications of this scientific discovery? May we continue killing lice? Should we abstain?

There are two basic approaches regarding the first question, with some saying that the science in Talmud were based on their own observations and therefore fallible, while others insisting on the infallibility of Hazal in science. These two groups have been dubbed by some “The Rationalistic School” and “The Traditionalistic School”. 


Within the Traditionalists, who posit that Hazal are infallible in matters of scinece, several approaches arose as to how to deal with the contradictions between Hazal and science. One approach is to say that nature has changed. Lice used to reproduce spontaneously, but have ceased to do so since. Another approach posits that Hazal referred to a different species of lice, not our every-day head-lice. Yet a third, somewhat extreme approach is to invalidate science altogether.


A third school of thought, which as per Bar Uryan's suggestion in the comments I shall refer to as “synthesists” (since they synthesize elements of both the rationalistic and traditionalistic schools), takes the following approach: Hazal did not at all refer to the physical reality, rather they discuss a distinct "Halakhic reality" so to speak. In our example of killing lice on shabbat, their approach will be that Hazal allowed it because the eggs are to small to be seen with the naked eye, and anything not visible to the naked eye is considered non-existent, at least as far halakha is concerned. The followers of this approach take no stance on the "did Hazal know modern science" question. It is irrelevant, for according to them there is a distinct halakhic reality according to which the halakha was determined regardless of the factual reality. A similar approach, which I will also include under this term, says that Hazal didn't refer to the physical reality, rather they spoke about an inner metaphysical reality. This approach is very similar to the above approach that there is a distinct halakhic reality, the only difference being that it does not seek to explain this halakhic reality in terms of physical explanations like saying that halakha does not concern itself with invisible reality and therefore lice-eggs are non-existent according to halakha. Rather, this approach posits that lice do not sexually reproduce in some metaphysical form which does not have any bearing on its physical reality. 
    
 All in all, these approaches deal with the first question only.

The second question is far more complicated. In the classic poskim, there’s much less consistency when it comes to deal with this question than with the first question. The basic approaches can be summarized as follows. In the Rationalistic School, we have two opposing approaches. One approach says that since we now know better, we must change the halakha, at least in a case where Hazal’s errant science leads to a leniency. For example, in the case of killing lice on Shabbat, this approach says we should abstain from killing them, since the leniency of Hazal that one could kill them is based on errant science. We’ll call this class of thought “reformists”. The second approach says that even though Hazal were mistaken, we must accept their halakhic rulings, even in place of a leniency. The explanation of this is that due to the power of so-called “canonizing” of halakha that Hazal possessed, we cannot uproot their halakhic rulings, even when the rulings were based on false data. According to this approach, we sure can go on killing on Shabbat those annoying little creatures messing with our hair. For the sake of simplicity, we shall dub this class “conventionalists”.

The Traditionalistic School also gets divided in two on this matter. According to the approach that say “nature has changed” or that we do not know what species Hazal were talking about, of course in theory the halakhah remains the same. But practically, we have to change the halakhah since nature has changed, or because we now have different lice species rummaging in our hair. The ones in this class are the “rectifiers”. (If you have a better idea for name, feel free to let me know in the comments!) But according to the approach that Hazal refer to an inner reality invisible to the naked eye, or the approach that science cannot contradict Hazal and is therefore wrong, the halakhah remains the same in reality. This class I will call “conservatives”.


Most of those who follow the "synthesists" approach that there is a so-called "halakhic reality", agree that the halakha does not change in light of modern scientific discoveries, since the halakha was not determined according to external scientific knowledge in the first place. (I'm indebted to Dov for pointing this out to me below in the comments.) This is definitely true for those who say that Hazal refer to a metaphysical reality.

This basically sums up the different opinions in the Hazal vs. reality debate. And in future posts dealing with issues related to this debate, keep in mind that when I refer to conservatives I’m not at all referring to members of the right wing political party in the United States.