How can one tell the difference between Chidushei Torah and words of a heretic?

Question

I was intrigued by this recent M.Y. question and its answers that suggest that one is encouraged to develop his own chiddushei Torah.

This had me thinking about what Talmud Chagigah 15a-b (excerpt here) relates about Elisha ben Avuya who eventually became a heretic. It relates a conversation that he had with his student Rabbi Meir. Elisha asks him about his interpretation of several verses. Then, Elisha refutes him and gives another explanation that, offhand, sounds valid.

If one were, say, studying with someone else and his friend offered a novel explanation, how would one be able to evaluate if it was valid or the words of a heretic similar to Elisha ben Avuya?

Note: While I'm citing the example of Elisha ben Avuya, please generalize your answer regarding dealing with anyone.

Answer 1

One approach is discussed in the continuation of the Gemara in Chagiga:

But how did R. Meir learn Torah at the mouth of Aher? Behold Rabbah b. Bar Hana said that R. Johanan said: What is the meaning of the verse, For the priest's lips should keep knowledge, and they should seek the Law at his mouth; for he is the messenger of the Lord of hosts? [This means that] if the teacher is like an angel of the Lord of hosts, they should seek the Law at his mouth, but if not, they should not seek the Law at his mouth! — Resh Lakish answered: R. Meir found a verse and expounded it [as follows]: Incline thine ear, and hear the words of the wise, and apply thy heart unto my knowledge. It does not say, ‘unto their knowledge’, but ‘unto my knowledge’. R. Hanina said, [he decided it] from here: Hearken, O daughter, and consider, and incline thine ear; forget also thine own people, and thy father's house etc. The verses contradict one another! There is no contradiction: in the one case Scripture refers to an adult, in the other to a child. When R. Dimi came [to Babylon] he said: In the West, they say: R. Meir ate the date and threw the kernel away. (Soncino translation.)

In other words, until one has reached a certain level of intellectual maturity one must be very careful about whom he learns from, precisely because it is difficult to distinguish the good from the bad.

Answer 2

There are a couple of points in your question which should be clarified. If you consult the Gemarah you cite I believe your reading is not accurate. Elisha did not refute anything R' Meir said, he only countered that R' Meir's teaching was not in accord with the way R' Akiva, R' Meir's teacher, learned. AFAIK nothing Acher says there is heretical.

In terms of your question, assuming (and this is a big assumption) that the Rambam's 13 principles of faith are binding, then the listener would merely need to know if what s/he is hearing violate those principles. In a recent Jewish Action article (starting on page 55) Rabbi Weiderblank makes the assertion that if a novel interpretation goes against the basic gist of how something has been interpreted for millennia; for example if one were to propose that Esav was a complete tzaddik, even if this assertion is logical and sourced in the verses it would be heretical.