People with more than a passing interest in words fall into two groups: prescriptivist and descriptivist. The prescriptivist believes that there is an ideal of correctness in the use of words, shifting and temporally-based as it ultimately may be. The descriptivist finds the concept of "correctness" elitist at best. More often, he finds it incomprehensible.
The one inviolable rule of descriptivism is this: there are no correct definitions, meanings, or usages other than those used by people-in-general; any attempt to impose some other definition is invalid. Where the prescriptivist subordinates popular usage to correctness, the descriptivist rejects all other criteria except those used by people-in-general.
Now consider what happens when you ask a descriptivist how he defines "dictionary."
The descriptivist might, as his inviolable rule says he must, accept the popular definition of "dictionary." If he does this, he will have to define "dictionary" in the commonly accepted sense of a book giving correct definitions that are determined by a literary elite. This, after all, is what most people mean when they say "dictionary." The descriptivist must accept the common view that there is a correct usage—in this case correct definitions—because his inviolable rule requires that he accept the view of people-in-general. In granting that there is a correct...