A good example of how communication breaks down when we begin to change the agreed-upon meanings comes from Lewis Carroll's Through the Looking Glass, when Alice encounters Humpty Dumpty:
'And only one for birthday presents, you know. There's glory for you!Humpty takes a common word and makes up an entirely different meaning for it. If I were to ask you to pass me that apple, you'd be rightly confused if I got upset that you handed me an apple instead of a wrench. Yet this is a behavior that seems to be fairly common among those who strongly oppose vaccinations.
'I don't know what you mean by "glory",' Alice said.
Humpty Dumpty smiled contemptuously. 'Of course you don't — till I tell you. I meant "there's a nice knock-down argument for you!"'
'But "glory" doesn't mean "a nice knock-down argument",' Alice objected.
'When I use a word,' Humpty Dumpty said, in rather a scornful tone, 'it means just what I choose it to mean — neither more nor less.'