We can't know what Humpty means because he says that only he determines the meanings of his words, and we can't read hhis mind. But if he means what he appears to mean, he'll soon be in a mental hospital either because no one will understand what he means, or else because he thinks his mind controls what everybody else means.

The functional meanings of words are determined by common consent, not by individuals. Though not everything is quite so simple, "chair" means "chair" because we agree that it does. In most languages, the sound of the word "chair" means nothing at all.

Of course, "common consent" varies and changes, sometimes helpfully direction, sometimes in quite the opposite direction. Except in technical fields (where "electron" better mean "electron" all the time), it's almost impossible to restrain changes in meaning. What's more, inconsistent meanings often exist at the same time. They rise and fall beyond the control of any group of individuals. Or individual.