Never imagine yourself not to be otherwise than what it might appear to others that what you were or might have been was not otherwise than what you had been would have appeared to them to be otherwise.
The Duchess is in one of her “moral” moods, offering advice that sounds wise and tangled at the same time. The sentence pushes Alice (and us) to think about being true to one’s appearance and conduct—“seeming” versus “being.” As an aphorism, it compresses a life-rule into a single, highly layered statement, which mirrors the book’s play with logic. The Reflective mood fits because the line asks for inner checking rather than outward show. Thematically it’s about Identity: how to align the self you feel with the self others perceive. Wonderland uses such knotty phrasing to make Alice wrestle with meaning, a practice run for adult ambiguity. Readers hear a universal nudge: integrity is messy, but consistency between self and act is worth the work.