Here is an extract from Isadore Twersky, “Joseph ibn Kaspi: Portrait of a Medieval Jewish Intellectual,” Studies in Medieval Jewish History and Literature, volume 1 (Harvard University Press, 1979), Isadore Twersky, ed., pp. 239-242:
Kaspi frequently operates with the following exegetical premise: not every Scriptural statement is rue in the absolute sense. A statement may be purposely erroneous, reflecting an erroneous view of the masses. We are not dealing merely with an unsophisticated or unrationalized view, but an intentionally, patently false view espoused by the masses and enshrined in Scripture. The view or statement need not be allegorized, merely recognized for what it is. Where did such a radical hermeneutic originate? How could Kaspi validate such an unusual methodological construct?
The key factor is Kaspi's use of the well-known rabbinic dictum: dibrah Torah bileshon bene adam, "The Torah speaks in the language of men," famous for its medieval use in the realm of anthropomorphism. Actually, in its original context, this statement, a cardinal rule of the school of R. Ishmael, applies to a wide range of grammatical-lexical-interpretive issues but never to anthropomorphism. Maimonides, foreshadowed by R. Judah ibn Koreish, R. Nissim Gaon, R. Abraham ibn Ezra, is responsible for converting this dictum into the basis and rallying point for all anti-anthropomorphic interpretations.
"You know their dictum that refers in inclusive fashion to all the kinds of interpretation connected with this subject, namely their saying: “The Torah speaks in the language of the sons of man." The meaning of this is that everything that all men are capable of understanding and representing to themselves at first thought has been ascribed to Him as necessarily belonging to God, may He be exalted. Hence attributes indicating corporeality have been predicated to Him in order to indicate that He, may He be exalted, exists, inasmuch as the multitude cannot at first conceive of any existence save that of a body alone... In a similar way one has ascribed to Him... everything that in our opinion is a perfection in order to indicate that He is perfect in every manner of perfection and that no deficiency whatever mars Him. Thus none of the things apprehended by the multitude as a deficiency or a privation are predicated of Him."
As Maimonides continues to establish the foundations for his theory of attributes, he parenthetically defines leshon bene adam: "However, in accordance with the language of the sons of man, I mean the imagination of the multitude." In its Maimonidean adaptation, the rabbinic dictum may then be paraphrased as follows: "The Torah speaks in conformity with the imagination (and frequently crude perception) of the multitude" and therefore uses anthropomorphic imagery when speaking of divine attributes.
Now, Kaspi rather boldly takes a third step and more or less systematically extends the parameters of this philological principle to include issues and problems totally unrelated to anthropomorphism. In so doing, he converts it from a pedagogic principle which provides a license for allegorical interpretation to an hermeneutical principle which provides a lesson in what we would call historicism. Many scriptural statements, covered by this plastic rubric, are seen as errors, superstitions, popular conceptions, local mores, folk beliefs, and customs (minhag bene ‘adam), statements which reflect the assumptions or projections or behavioral patterns of the people involved rather than an abstract truth. In its Kaspian adaptation, the rabbinic dictum may then be paraphrased as follows: “The Torah expressed things as they were believed or perceived or practiced by the multitude and not as they were in actuality.”
...Leshon bene adam is not just a carefully calculated concession to certain shortcomings of the masses, that is, their inability to think abstractly, but a wholesale adoption of mass views and local customs... The Torah did not endorse or validate these views; it merely recorded them and a proper philosophic sensibility will recognize them... Leshon bene adam, which insists that the text be interpreted in accord with all rules of language as well as all realia, including folk beliefs, enables the exegete to sustain a literalist-contextual approach, thus obviating the need for excessive allegory and yet not doing violence to philosophic conviction... [Ibn Kaspi] proposes an alternate exegetic procedure, simple yet far-reaching, which will yield a literal understanding of the text without adding or emending or shuffling. This procedure combines exegetical naturalism — trying to understand everything in the context of ordinary experiences — and historicism — noting cultural realities, differences in manners, habits, geography, expression.
You can download the full article here. Note that Ibn Kaspi's approach was also discussed by Joel B. Wolowelsky, “A Note on the Flood Story in the Language of Man,” Tradition 42:3 (Fall 2009) pp. 41-48.