When you start engaging in the language wars—any area of English that is contested—you soon encounter the terms “descriptivist” and “prescriptivist.” Ironically, these two words are also the subject of debate, so let’s take a closer look at them.

A descriptivist is generally speaking, a practitioner of linguistics who is more interested in why people say what they do, and who would maintain that if a native speaker says something, it’s almost assuredly grammatical. For example: “They asked me to carry the severed head but I ain’t doin’ that.” From a descriptivist standpoint, the word “ain’t” is an informal contraction of “am not,” and the shift in tenses between “asked” and “ain’t” suggest the speaker’s meaning is that not only did refusal occur in the past, but it would occur on any subsequent occasion. Notable persons in this category include Stephen Pinker, Noam Chompsky, and John Searle.

A prescriptivist, on the other hand, is more focused on proper English in its standard variety, and believes that by upholding traditional rules and standards clarity and effectiveness of communication can be maximized. To take the previous example, a prescriptivist would object to “ain’t” as being non-standard, and would argue for, “They asked me to carry the severed head but I wouldn’t do so under any circumstances.” (Or any equivalent variant of this.) Popular prescriptivists include Lynne Truss and Nevile Gwynne.

Commonly, you’ll see these two position on the English language presented as if they are two sides in a linguistic tug o’ war, each vying for supremacy. This isn’t the case, however, because descriptivists aren’t advocating for any particular type of usage; they want to explain what a speaker is doing. Prescriptivists, for their part, want to answer the question, “What’s the best way of saying this?”

Petitio principii

This Latin term is usually translated as “begging the question.” Formally, it means committing the fallacy of a circular argument, e.g., “Lobsters are cheap right now because nobody likes lobster.” This asks the listener to accept the premise that lobster is unpopular, whereas there could be alternate explanations, such as a glut in their availability. A prescriptivist would maintain this distinction, but a descriptivist would be more likely to point out that in observed usage, in well more than 90 percent of observed cases, “begs the question” is used in the sense of “raising the question.”

You can see the sense of both approaches, because petitio principii is a useful term that describes a rhetorical fault, yet at the same time few speakers would understand you if you used it that way. You’ll see similar effects with “to coin a phrase,” and “the proof is in the pudding,” both of which are rarely used in the traditionally correct form.

The wisdom of the crowds

Ultimately, each language user gets one vote, and the rules of English and the meaning of words is what the group collectively decides they are. Editors and careful writers, and those aiming their text at academic and formal audiences, will tend to accept linguistic change at a slower rate and hew to traditional standard English as long as possible. Finally, when the group consensus is clearly overwhelming, a change becomes acceptable across the board. As a case in point, newspaper style used to maintain that numbers could increase or decrease, but not have positional state, so that “Over 50 people were at the protest” was a fault, and a copyeditor would change it to read “More than 50…” etc. It was only in 2016 that the editors of the Associated Press finally relented when they realized they were among a minority still observing this distinction.

The right tool for the job

When you are more interested in meaning and the purpose of language, if you want to know what most people do and why they do it, consult more formally linguistic sources. Websites like the Lingua Franca blog and the blog at Grammarphobia are reliable. John McIntyre’s blog You Don’t Say is accessible and entertaining.

On the other hand, if your concern is with what “the right thing” is in a given situation, such as whether to use “affect” or “effect,” “lie” or “lay,” then you don’t particularly care how commonly people misuse them—you just want to know which one is correct. Here’s where you might turn to Patricial O'Conner's Woe Is I, or the Chicago Manual of Style. Whether to take a more prescriptivist or descriptivist tack depends on what you are trying to accomplish; these are not philosophical positions on a scale from “rigid to permissible,” rather, they are different lines of inquiry. Pick the right tool for the job.