Chiasmus

Chiasmus, from the Greek khiasmos, "crossing," for the letter chi, is "the reversal of grammatical structures in successive phrases or clauses without repetition of words": parallelism turned back on itself in an A-B-B-A shape. The article's account of why it lands: it "derives its effectiveness from its symmetrical structure," imposing "the impression upon the reader or listener that the entire argument has been accounted for." Its examples: Othello's "Who dotes, yet doubts; suspects, yet strongly loves," Johnson's "By day the frolic, and the dance by night." The near neighbor antimetabole "also involves a reversal of grammatical structures" in the same shape but, "unlike chiasmus, presents a repetition of words."

For the novelist chiasmus is a sentence that closes like a clasp, two clauses folding into balance; it is juxtaposition given syntax and the turned-around cousin of the repetition device anaphora.