In a review essay of One People, Two Worlds in The Torah U-Madda Journal, Dr. William Kolbrener posits that a central dispute between the two adversarial authors of the book is based on a faulty premise. Rabbi Yosef Reinman, the Orthodox author, takes the stance that the Torah (in its broad sense) teaches absolute truth about the world. Reform rabbi Ammiel Hirsch argues that truth is relative. Dr. Kolbrener submits that the two authors are mired in a world dominated by Greek categories of thought while the Torah exists outside of that world. The Torah is neither absolute truth nor relative truth; it is interpretive truth. As the Ritva (Eruvin 13a) explains, multiple positions were given at Sinai and they are all true. There is absolute truth but it is in multiple forms. One can be wrong by taking a position not given at Sinai, but differing parties can still hold different absolute truths. Dr. Kolbrener suggests that the Maharshal (introduction to Yam Shel Shlomo on Bava Kama) agrees with this approach.
Be that as it may, the Ran disagrees. A careful reading of the Derashos Ha-Ran (Feldman ed., pp. 43-45, 84-86, 111-114) reveals that while he believes that there is a multiplicity of views in the interpretation of Torah, only one view represents absolute truth. It is our job to use the methodologies of Torah to find the best truth that we can. However, it is possible for us to fail and to espouse a position that is "the opposite of truth." Even if we do so, as the Sages did in opposition to R. Eliezer regarding the oven of Akhnai, we are still obligated to follow the position to which our methodologies lead. I interpret this position as follows. There is an absolute truth, however it is in heaven. We have the methodologies of Torah with we which can try to approximate truth and that approximation is the best humanly possible given our limitations. We are to treat that approximation as the truth even if we have information from outside of our accepted methodologies of approximation. "It is not in heaven" because we live in a world of approximate-truth and the world of absolute truth is beyond our grasp.[1]
This might possibly be the intent of the Maharal.[2] According to the Maharal, all positions have an element of truth in them even though one is more true than others. This could be translated into my terminology as meaning that all (validly arrived at) positions are legitimate approximations of the truth even if one represents the absolute truth.[3]
Given all this, and, truly, even given the Ritva's approach, the argument between Reinman and Hirsch is not over what is absolutely true and what is not, but over what methodologies are sufficiently legitimate to result in a version or an approximation of truth and what are not. Hirsch would allow any and all methodologies to undermine even the most basic of faiths while Reinman is much more restrictive and conservative in his acceptance of methodologies. To use an example from their book, Hirsch would label as true an approach that allegorizes Sabbath observance while Reinman would not countenance ignoring millennia of Jewish precedent and an entire talmudic tractate about the laws of Shabbos. Could that, Reinman would presumably ask, have been one of the truths given at Sinai?
A potential difference between the Ritva/Maharshal approach and the Ran/Maharal approach is as follows. If a view was given at Sinai then, according to the Ritva, it is true regardless of what later generations believe. However, according to the Ran, it is only valid if it is within acceptable methodologies. If a methodology declares that something is "einah Mishnah," according to the Ritva it cannot lose its status of true. Either it was true and remains so or it was never true. Once it is established that it was once true it will always retain that status. According to the Ran, however, that need not be so. Something may be considered an approximation of truth at one point in time and then later disqualified from being considered an approximation.
[1] See also Sefer Ha-Hinukh 496 and Or Hashem 3:5:2.
[2] Be'er Ha-Golah pp. 19-20, cited in R. Michael Rosensweig, "Personal Initiative and Creativity in Avodat Hashem" in The Torah U-Madda Journal vol. 1 pp. 80-81.
[3] In a different essay, R. Michael Rosensweig writes "[Maharal's] comparison of halakhic categories and institutions to the human personality and its manifold complex characteristics suggests a kind of Platonic model which presupposes the existence of an ideal halakhic status which precedes and supersedes the sum of its components... Thus, one may speak of approximating the ideal sufficiently but not fully, and the same token substantially but not sufficiently, and consequently, a whol hierarchy of truths would emerge."