For this evidence is dramatically in agreement with the hypothesis. Amos is almost pure bicameral speech, heard by an illiterate desert herdsman, and dictated to a scribe. In Ecclesiastes, in contrast, god is rarely mentioned, let alone ever speaking to its educated author. And even these mentions are considred by some scholars to be later interpolations, to allow this magnificent writing into the canon.
In Amos there are no words for mind or think or feel or understand or anything similar whatever; Amos never ponders anything in his heart; he can't; he would not know what it meant. In the few times he refers to himself, he is abrupt and informative without qualification; he is no prophet, but a mere "gatherer of sycamore fruit"; he does not consciously think before he speaks; in fact, he does not think as we do at all: his thought is done for him. He feels his bicameral voice about to speak and shushes those about him with a "Thus speaks the Lord!" and follows with an angry forecful speech which he probably does not understand himself."
Ecclesiates is the opposite on all these points. He ponders things as deep in the paraphrands of his hypostatic heart as is possible. And who but a very subjective man could say, "Vanity of vanities, all is vanity," (1:2), or say that he sees that wisom excels folly (2:13) One has to have an analog "I" surveying a mind-space to so see. And the famous third chapter, "To everything there is a season, and a time to every purpose under heaven. . ." is precisely the spatialization of time, its spreading out in mind-space, so characteristic of consciousness as we saw in l.2, Ecclesiastes thinks, considers, is constantly comparing one thing and another, and making brilliant metaphors as he does so. Amos uses external divination, Ecclesaiates never. Amos is fircely righteous, absolutely assured, nobly rude, speaking a blustering god-speech with the unconcscious rhetoric of an Achilles or a Hammurabi. Ecclesiastes would be an excellent fireside friend, mellow, kindly, concerned, hesitant, surveying all of life in a way that would have been impossilbe for Amos.
These then are the extremes in the Old Testament. Similar comparisons can be made with other early and late books, or early and late parts of the same book, all revealing the same pattern, which is difficult to account for apart from the theory of the bicameral mind.