The linguistic theme of Through the Looking Glass, the narrative's critique of signification (e.g. Alice's mention of names as objectifying strategies in the "Looking Glass Insects" episode; "the wood where things have no names"; Prof. Dumpty's discourse on language), conforms nicely to the work's overall mirror theme. For Carroll is criticizing the received idea of language as a reflection of the world, a mirror of nature (to invoke Rorty's title phrase), in a way that uncannily anticipates Saussure, Derrida and even Foucault. This is very high nonsense, indeed. An academic could write an article titled "Disturbing Reflection: Lewis Carroll's Critique of Language"...
This critique of language, while intellectually 'radical,' is considerably less subversive than Alice in Wonderland's Swiftian satire of the structures of bourgeois life in Victorian England, its rules, rituals and characteristics (tea, croquet, trials, the sanctity of motherhood, moralistic poetry, etc.) It's interesting that the movement between the two books parallels the trajectory of academic 'radicals' in the post-1960's U.S., from a fundamental critique of society's material base to the criticism of its texts and language. Lewis Carroll made his own 'linguistic turn,' it seems.
Looking Glass is, on balance, a slightly lesser work than Wonderland, lacking the latter's imaginative exuberance, its sense of 'anything can (and likely will) happen.' Looking Glass is a more deliberately structured work,a bit more labored, seemingly less inspired. It does, however, contain many things equal to the best of Wonderland, and there is probably no higher praise than that. Unfortunately, the weakest point of Looking Glass is its climactic chapter, where only the dinner party is up to Carroll's usual standards of invention. If a short work must have a slack chapter, the climax is its worst possible location; Carroll leads us on a wonderful journey, then spends several static pages boring us near the end. Why? It's damn bad craftsmanship, that it is, as M. Dumpty might say (in his W.C. Fields persona).
Both books deeply, deeply impress me (as they have for years now). They are the most fabulously inventive, intelligent, original books ever written for children; they're also a rare Victorian link in the line that connects Swift and Sterne to Joyce and Rushdie.