Fundamental pattern:  two becomes one becomes two becomes one. . .

Birkin (ch. 23, "Excurse"): "Fusion, fusion, this horrible fusion of two beings, which every woman, and most men insisted on, was it not nauseous and horrible anyhow, whether it was a fusion of the spirit or of the emotional body? . . . Why not leave the other being free, why try to absorb, or melt, or merge? One might abandon oneself utterly to the moment, but not to any other being."

Application:  to virtually all interpersonal relationships in the novel (characters tend to come in pairs), but also to conceptual dichotomies (e.g., Birkin's confused discourse on a "river of life" and "river of dissolution" in "Water-Party," where the 2 seem to become 1.  Sometimes "dissolution" and "corruption" precede rebirth; sometimes it doesn't.

In a classic dialectic, thesis confronts antithesis and he contradiction is kicked up to a higher level in a fusion of thesis and antithesis. A vs. B -> A'B'. Or, imagine a scene in which a man is trying to force a woman to tell the truth in response to the question, "Who is that girl?" "My sister," she replies, and he slaps her, believing her not to have a sister. "My daughter," she replies, and he slaps her again, believing her not to have a daughter. "My sister" — slap — "My daughter" — slap — and so on until she finally breaks down, revealing the dialectical truth: "She's my sister and my daughter." And the horrible truth of the new synthesis dawns on him.

Application:  Birkin/Lawrence believe that modern civilization, in part owing to the influence of Christianity and dehumanizing technology, is devolving and has produced both an atrophy of our physical, sensual, passional being and a hypertrophy of our  mental, analytic, rational being. Thus Birkin in "Classroom", asked if he truly wants "sensuality": "Yes," he said, "that and nothing else, at this point. It is a fulfillment — the great dark knowledge you can't have in your head. It is death to one's self — but it is the coming into being of another." A dialectical synthesis of the cleavage between mental and sensual is not the pattern of action and reaction between the "spiritual" and a vaguely obscene something else described by Hermione in "Woman to Woman" but, in Birkin's words, "knowledge in the blood" or "blood brotherhood"; or in DHL's words in the letter to Russell, it is "blood consciousness" — at once physical and aware.

The positive version is apparently what Birkin wants to realize with Ursula — "ultimate marriage" incorporates ("In the Train"), it would seem, the ideal synthesis represented by "blood consciousness," unlike the apparently different relationship he had with Hermione, which as Ursula points out repeatedly and at the top of her lungs in "Excurse," was "perverse . . . dirt." But the negative synthesis of mental and physical is always ready to rear its ugly head, sometimes in the form of  "the loathsome little skull" of Hermione, who doesn't (according to Birkin) "want to be an animal, you want to observe your own animal functions, to get a mental thrill out of them" ("Classroom"). Or the negative synthesis surfaces more spectacularly in the dark rites of "Rabbit": "it was as if he had knowledge of her in the long red rent of her forearm, so silken and soft. He did not want to touch her. He would have to make himself touch her, deliberately. The long, shallow red rip seemed torn across his own brain, tearing the surface of his ultimate consciousness, letting through the forever unconscious, unthinkable red ether of the beyond, the obscene beyond." For DHL, "positive" in this context would mean "true," and "negative" "false"; or perhaps "ideal" and . . . "literalized"?