I-C. 1. It would seem that an investigation into the source(s) and quality of Chazal's scientific knowledge ought to be primarily historical, as opposed to halachic. Any particular sage either held a certain belief (belief in spontaneous generation, for example), or did not. He either derived all of his scientific knowledge from the Written Torah and oral tradition, or he employed other sources as well. The truth of the matter is not subject to moral or halachic arguments. It happened in a particular way; which way that was is a question of historical fact. We should attempt to resolve that question – if we wish to do so truthfully – not via the usual method of halachic ruling, but by examining the relevant historical evidence, assigning each piece its appropriate weight. Therefore, by way of example, it would seem appropriate in this matter to assign greater weight to the opinions of the Geonim – who lived closer both in time and in location to Chazal – than we would in a typical halachic debate, where they might be more easily trumped by later, European authorities such as Rashba, Rivash or Rema.
2. I have limited this investigation, somewhat arbitrarily, to the question of Chazal's scientific knowledge. I see no reason, however, to assume that the quality of their scientific knowledge was different from the quality of, for example, their historical knowledge. Thus if we conclude that they relied on the science of their times, with its flaws, for their scientific knowledge, we may then be justified in supposing that they relied on the historical beliefs of their times – accurate or inaccurate, complete or incomplete, as they may have been – for their historical knowledge. This conclusion, if warranted, may be instructive in resolving contradictions between certain historical assertions of the Talmud and the findings of modern archaeology, such as the dating of the construction of the Second Temple.
3. Occasionally a post-Talmudic authority appears, in different passages, to adopt conflicting approaches to the authority of Chazal's science. I believe that one must evaluate each of these apparent contradictions on a case-by-case basis. Sometimes it may prove that there is not really any contradiction. In other cases, the author may have changed his mind. It is also possible that he wrote different things for different audiences or in response to different circumstances; this is not unknown in rabbinic literature.
One general rule of which I am reasonably confident is that a genuine Torah scholar is far more likely to exaggerate Chazal's strengths than their weaknesses. I would not necessarily assume that a statement like "Chazal knew all science" was believed literally by the author, even if he did not contradict it elsewhere in his writings. In contrast, if an orthodox scholar states that Chazal erred in one of their scientific pronouncements, or that they were capable of error, I am inclined to think that he really believes it; for otherwise, his assertion constitutes inexcusable irreverence. This principle will be, I imagine, intuitive to anyone familiar with rabbinic texts.
All things being equal, then, in cases where two passages contradict each other and it seems that one of them does not accurately represent the author's belief, I am more inclined to think that one passage exaggerates Chazal's scientific competence than that the other falsely and gratuitously accuses them of error.
4. Rabbi Dr. Dovid Gottlieb of Ohr Somayach has written an excellent essay entitled "Living Up to the Truth" (available at www.dovidgottlieb.com/works/truth97.doc) regarding the grounds for rational belief in the veracity of the Torah and of orthodox Judaism. Very generally, he argues that many ascertained historical facts associated with the Torah are so exceptional and unprecedented as to defy any reasonable natural explanation. It is more rational, he asserts, to assume supernatural intervention as the cause of these historical anomalies; this assumption leads to the conclusion that there is a God, and that God gave the Israelites the Torah. (Obviously, his essay, more than sixty pages long, has hardly been done justice in my two sentences here.) I wish to examine briefly what bearing this approach to belief in Judaism may have on our topic of Chazal's scientific knowledge.
The crux of Rabbi Gottlieb's argument is that although the divinity of the Torah cannot be proven beyond all possibility of refutation, divine authorship is the most reasonable explanation of its provenance. The evidence in favour of divine authorship overwhelms the evidence against it. Thus, although we may have difficulty believing, for example, the Torah's report that manna fell from heaven for forty years to feed the Jews, the alternative – believing that this account in the Torah is false – is even more unreasonable, and we must therefore accept the truth of the Torah's claim.
Let us now perform the following mind experiment. Suppose the Torah said – without allowing for any possibility of interpreting its assertion non-literally – that Bill Clinton had never existed (and never would exist). What impact would this statement have on our assessment of its credibility (and, hence, its divinity)? I propose that the evidence in favour of the existence of Bill Clinton outweighs the evidence Rabbi Gottlieb presents in favour of the Torah's divinity. Thus if acceptance of the Torah's truth requires us to deny the existence of Bill Clinton – as it does, in our case, by construction – we must, if we are rational, reject instead the reliability of the Torah and maintain our belief in Bill Clinton's existence. We will have to find other ways to explain the historical anomalies associated with the Torah.
Suppose now that the Torah – or its extension, Torah Judaism (see Rabbi Gottlieb's essay) – required us to believe that spontaneous generation of living organisms occurs on a regular basis; or, at least, that it did in the times of the Talmud. What impact would this statement have on our assessment of the Torah's credibility (and, hence, its divinity)? We would have to compare the evidence in favour of the Torah's divinity with the evidence against the regular occurrence of spontaneous generation. If the former outweighs the latter, we would conclude that spontaneous generation occurs, evidence to the contrary notwithstanding. Otherwise, we would be forced to accept that the Torah is false, and, again, we would have to explain away the historical evidence Rabbi Gottlieb presents.
I personally assume that Talmudic science was flawed, and understandably so, given that the greatest scientists of the Talmudic era had reached conclusions that later investigations have since disproved. I do not consider the imperfection of Talmudic science to invalidate the bulk of the Torah, the Talmud, or Judaism as a whole, since I do not believe the assumptions of Talmudic science to be part of the indivisible corpus of Jewish dogma that one must either accept or reject in its entirety. The list of sources that follows is partially intended to demonstrate that many of the greatest scholars in the last 1500 years of Jewish history have held the same view.