Why it's simply impassible! Alice: Why, don't you mean impossible? Door: No, I do mean impassible. (chuckles) Nothing's impossible!

The exchange hinges on a pun: “impassible” (not passable) versus “impossible” (not possible). The Door’s insistence on “impassible” turns a statement about logical impossibility into a physical, spatial problem—something that can be “passed” if only one finds the right way through. Carroll uses this kind of wordplay to satirize pedantic reasoning and to show how language can reshape reality in Wonderland: definitions are slippery, and authority (here, a talking Door) can win arguments by controlling terms. The final claim, “Nothing’s impossible,” reads as comic optimism, but also as a critique of how “impossible” often reflects limited imagination rather than true constraint.