When I use a word,” Humpty Dumpty said, in a rather a scornful tone, “it means just what I choose it to mean—neither more nor less.”
“The question is,” said Alice, “whether you can make words mean so many different things.”
“The question is,” said Humpty Dumpty, “which is to be master...that’s all.”
This bit of Lewis Carroll is used a lot in internet bust-ups but often wrongly. Some seem to think of it as an extension of Wittgenstein’s Private Language Argument, which demonstrated that a purely solipsistic language is an incoherent concept. In fact Humpty Dumpty is just a witty gag. A correct application in an argument would be to satirize a sophist who has deliberately equivocated between two different meanings of a word to make a single point, or who has wilfully misled by pushing the definition of a word beyond the commonly recognised boundaries of reasonableness, without indicating that he is doing so.
An incorrect application would be the circular argument whereby you assume a particular definition of an ambiguous word and, in the face of disagreement, produce the Humpty Dumpty. An even more incorrect application would be as a prop for the literalist idea that words have a single, universal, timeless definition. This is a category error and is obviously not the case because words change their meaning over time, have ambiguity, shades, double-meanings etc. They are frequently, perhaps usually, inadequate for containing reality. Commonly recognised boundaries of reasonableness are all we have. ‘Black’ and ‘white’, for example, are far from black and white when it comes to describing humans.
Poetry, most jokes and word-coinage would also be impossible if words were ‘objective’ in the scientific or Platonic sense, rather than the ‘generally agreed’ sense (thus ‘objective’ is itself an example of the problem). A good counter-argument to the misapplication of Humpty-Dumpty is another bit of Lewis Carroll. Who is the master here?
’Twas brillig, and the slithy toves
Did gyre and gimble in the wabe;
All mimsy were the borogoves,
And the mome raths outgrabe.