On the surface, “I mean what I say” is an offended insistence that the Mock Turtle’s words are already correct. But the line does more than defend a joke. It asserts a Wonderland principle: meaning is not negotiated by shared usage but decreed by the speaker’s intention at the moment of speaking. Alice’s suggestion—substituting “purpose” for “porpoise”—appeals to conventional language. The Mock Turtle’s reply refuses that appeal and elevates a pun to literal truth within the scene’s logic: if he said “porpoise,” then a porpoise is what he meant, and therefore what the situation contains. The claim echoes the chapter’s pattern of mock explanations: the Gryphon’s boot-polishing “whiting,” the shoe-leather “soles and eels,” and the dance “figures” whose steps are arbitrarily fixed. In this environment, a word’s sound can overrule its dictionary sense. The line thus dramatizes Carroll’s satire of pedantic talk that insists on correctness while evacuating meaning, and it marks Alice’s growing awareness that arguing for ordinary sense is futile in a world where language behaves like a game with skewed rules.