When Chazal make a statement, how do we know whether to interpret it literally or allegorically? I would like to describe different methodologies, with reference to the Gemara's statement that the kidneys give counsel, presenting four different approached. I will begin with my own methodology (which I shall call "Approach #1"), which involves asking three questions:
1) What light does the textual context shed upon it?
In the case of the kidneys, the surrounding statements about the function of the tongue, mouth, esophagus, windpipe and so on, are all literally true. This means that, absent overwhelming evidence otherwise, the description of the liver causing anger and the kidneys giving counsel is also intended literally.
2) What light does the historical context shed upon it?
Some people assume that if Chazal's statement is obviously incorrect at a literal level, then it must have been intended allegorically. Yet the question to ask is not whether it appears incorrect to us, but rather if it would have appeared correct back then. Now, we know that in Aristotle's view and other prevalent views in the ancient world, all thoughts and emotions were thought to take place in one's heart, kidneys and liver. Thus, when Chazal make such statements, they were presumably speaking literally - especially since people at that time would naturally interpret Chazal literally, and Chazal would surely not have been deliberately misleading them.
3) How do the Rishonim interpret it?
In general, the Rishonim were closer to Chazal's cultural worldview than were the Acharonim. Furthermore, they were not biased by an attempt to make Chazal conform with modern science - since modern science did not exist yet. So I place far greater weight on the interpretation given by the Rishonim than on that given by the Acharonim. (Incidentally, the Rishonim themselves, in deciding when to interpret Chazal literally and when to interpret them allegorically, were probably using the first factor that I discussed, as well as being influenced by the second.) In the case of the kidneys, the Rishonim all interpret Chazal literally - although Ramban and Rabbeinu Bachya, who had already accepted Galen's discovery that the brain is used for thought, had to make a curious hybrid of Chazal and Galen, in which thought begins in the brain but is "actualized" in the heart and kidneys, which send instructions to the rest of the body.
Now, let us turn to the approach of those who interpret Chazal allegorically. The case of the kidneys is particularly interesting, since there are two ways of interpreting it non-literally: that it literally refers to the kidneys, but does not literally mean that they give counsel; or that it literally means that something give counsel, but does not literally refer to the kidneys.
The former approach (Approach #2) argues that, of course, Chazal were literally talking about the kidneys, just as they were literally talking about the tongue, mouth, esophagus and windpipe. But, of course, Chazal did not literally mean that the kidneys advise the heart on what to do; what they meant is that the kidneys filter the urine, or that the adrenal glands which sit on top of the kidneys can affect serotonin in the brain which causes depression, or some other such minor function. (Those who adopt this approach do not explain why the Gemara is so misleading, why it omits any mention of the brain, why it says that the right kidney gives good counsel and the left kidney gives negative counsel, and what Scripture means when it says that God judges a person by examining his heart and kidneys rather than his brain.)
The latter approach (Approach #3) argues that of course Chazal are talking about actually giving good and evil counsel from which a person much choose, but of course Chazal were not actually talking about the kidneys, which do no such thing; rather, they were obviously talking about a spiritual component of man's soul which is merely allegorically described as being the "kidneys." (Those who adopt this approach do not explain why the Gemara is so misleading and misled all the Rishonim, nor do they give any reason as to how we actually know that the Gemara is referring to "spiritual kidneys.")
Then, of course, there are those who insist that Chazal were speaking entirely literally, and that they are actually correct. (This is really just a variation on Approach #1, but I shall number it approach #4 for convenience). This was the approach of many Rishonim, and also of certain Acharonim and recent figures (such as Chida, notwithstanding Rabbi Bechoffer's absurd reinterpretation of Chida).
What methodology lies behind these latter three approaches? What techniques do they use to determine when Chazal are speaking literally, and when they are speaking allegorically - and which components of their statements are literal, and which are allegorical? Simple. They use whichever interpretation gives the desired result: That Chazal are correct. If they feel that science supports Chazal, then they say that Chazal were speaking literally. If they feel that science partially supports Chazal, then they interpret Chazal's statement about "giving counsel" figuratively. And if they feel that science does not at all support Chazal, then they say that Chazal were "of course" not literally referring to the kidneys at all.
How do I know that this is their technique? Well, first of all, it's just obvious. This is exactly why, when I agreed to debate Isaac Betech about the scientific accuracy of Chazal's statements, I insisted that he first discuss the methodology for determining when Chazal are speaking literally, and when they are speaking allegorically. Needless to say, the debate did not materialize.
Second of all, it can be demonstrated by the fluid ease with which they slip from one approach to another, the way in which they are enthusiastic about all the other approaches apart from Approach #1, and the way in which they reinterpret earlier approaches. Rabbi Yosef Gavriel Bechoffer (RYGB) gives some superb illustrations of this. He claims that Ramban and Rabbeinu Bachya are actually saying that the kidneys and innards merely transfer information from the brain. This despite their clear words that, although thought is conceived in the brain, the kidneys and innards are actually responsible for the machshavah of a person's actions, for the actualization of these thoughts. And as for the Gemara's statement that the kidneys give counsel - RYGB makes an incomprehensible statement about Ramban and Rabbeinu Bachya not referring to this Gemara. And as for the scientific inaccuracy of saying that the kidneys transfer thought from the brain, and its incompatibility with the Scriptural accounts of God judging a person by examining his heart and kidneys - RYGB suggests that it is supported by the idea of the adrenal glands affecting serotonin levels! RYGB likewise claims that the Chida is talking about the adrenal glands affecting serotonin, even though the Chida plainly understands that the heart and kidneys are actually determining a person's actions in general. And he finds the approach of R. Yekusiel Kamelhar credible - a recent apologist whose approach is to say that the Gemara is allegorically referring to the "spiritual kidneys," which are so named because just as the actual kidneys serve "good eitzah" by filtering urine, so too the spiritual kidneys give good counsel (and bad counsel too, but this is not reflected in the nimshal, for unexplained reasons). RYGB seems to like all of these approaches, and only strongly protests my own approach, based on the careful three-stage analysis above, which he deems "flippant." In other words, he has no methodology at all - he just likes whatever approach will give the desired result of Chazal being correct.
There's a description of that: it's called "intellectual dishonesty." Now, I really don't get offended by people engaging in intellectual dishonesty. And I don't get my kicks by putting people down. But what irks me no end is when they use that as a podium from which to condemn others.