Grammarians of the prescriptive school take it as part of their task to distinguish correct from incorrect usage in language and thereby to encourage the former. They believe that in so doing they play an essential role in preventing a constantly changing language from falling into disarray. In contrast, descriptive grammarians are so called because they are content to describe the way language is actually used by members of a community. In their eyes, those who seek to preserve some forms of usage while preventing others from gaining a foothold are being unscientific and are, moreover, doomed to almost certain failure. Descriptivists point to numerous examples of usage that were once judged by prescriptivists to be incorrect but that over time and through continual use have come to be almost universally accepted. One example is the use of "data" as a singular noun in English: prescriptivists have typically regarded the phrase "the data is incomplete" as ungrammatical, on the grounds that "data" is the plural of the Latin noun "datum" and should continue to be treated as a plural in English out of respect for the word's origins. Descriptivists argue that "data," in addition to its use as a plural, has acquired a widespread use as a singular mass term, like "water." It would be pointless, they say, to try to reverse this trend.

This example illustrates the two main objections of descriptivists to prescriptivism. The first is the scientific objection: the transformation of language is governed by laws not unlike the laws of nature, and those trying to hold back linguistic change might as well attempt to defy the law of gravity. The second is the egalitarian objection: the prescriptivists are simply trying to impose their own linguistic practices, which are usually those of an educated and affluent elite, upon other members of society. The suggestion is that the attempted imposition is somehow immoral.

With regard to the scientific objection, it should be noted that while many attempts to regulate language have failed, some have succeeded. Descriptivists may respond that in the latter cases the usages favored by prescriptivists were in accordance with the laws governing linguistic change and would have prevailed without their assistance. But this is in large measure an article of faith. In the end it must be acknowledged that the laws governing the transformation of language are not like the laws of physics. Language usage depends on choices made by individuals, who are subject to persuasion. In response to the egalitarian objection, prescriptivists point to the importance of standard language usage for the free exchange of ideas. Those to whom preservation of the standard is entrusted inevitably possess some of the attributes of an elite, but their aim is one of inclusion rather than exclusion.