In simple terms, prescriptive grammar is the way society tells us to speak a language. As the phrase implies, you can think of it as a grammar prescription, a prescription being a list of things you should do—like the prescription for medicine that a doctor prescribes for you.
Descriptive grammar, in contrast, simply describes the way people actually speak.
However, these two terms have much more meaning, with important scientific and social implications.
Descriptive Grammar
First the question: what is grammar anyway?
Many people think that grammar means rules like “do not split infinitives,” “do not put a preposition at the end of a sentence,” and “a sentence must have a verb and a noun”—rules that we learn in school. They might even think that grammar includes spelling and punctuation. And if people do not follow these rules, they obviously have “bad grammar.” Some go so far as to view people with “bad grammar” as stupid or irresponsible. Distressingly, these are common attitudes.
But if all of those taught rules are grammar, then how do children and people ever learn language in the first place? After all, nearly every child learns language, without school, without instruction, and without much effort. Children learn to speak their first language, and often 2-3 languages, before ever setting foot in a classroom. And parents rarely teach their children any grammar rules outright. Yes, you might correct a child’s grammar errors sometimes, but children learn to speak languages fluently, almost entirely without explicit instruction.
And we rarely need to think, consciously, in order to speak our native language correctly. This ability to speak our native language is unconscious—and this unconscious knowledge is what linguists call the grammar of a language. Unconscious grammar is not a list of rules that was consciously created and passed along through a stable set of grammar lessons. Rather, it is a pattern in the brain that cannot be easily described—similar to the patterns in artificial neural networks created with machine learning by artificial intelligence. There is still quite a bit of mystery about how language is wired into the brain.
At this point, nobody consciously knows the full and true grammar of any language—not even linguists. This is one reason that linguists still have jobs. They are still trying to describe the true grammars of languages. Linguists look for patterns in the language of native speakers and try to describe those patterns as rules. But these rules are not the kind of rules that can be broken or followed. They are more like laws, as in the laws of physics. These “rules” are just descriptions of what native speakers do; this is descriptive grammar.
Prescriptive Grammar
As previously stated, prescriptive grammar basically means the rules we learn in school and other formal institutions. Most people, however, don’t observe such rules in their everyday speech, especially outside of formal situations, which is not surprising since these learned rules are not part of the unconscious knowledge that makes it possible to speak a language. One way to look at it is that we already have language before entering school, and we continue to have language long after.
Prescriptive grammars are like rules for social behavior—like the rules of politeness, clothing, and driving. We obey them so that other people will know that we are educated and approve of us—they are basically codes of social etiquette and reputation.
When you first learn that prescriptive grammar is not ‘true’ grammar, this may upset you; people are usually proud of following the rules they learned in school and believe that it makes them better or smarter people. In fact, this is probably the main reason that we have prescriptive rules of grammar in the first place—in order to show people that we are educated and belong to a better social and economic class. This is why the prescriptive rules that we learn in school only apply to a specific kind of language—standardized language, i.e., Standard English—the kind of language used in textbooks, on the television news, and in courtrooms.
Linguists have observed that this standardized language is always based on the dialect of the people with the most money and power in a society. In fact, linguists have a joke: “a language is a dialect with an army and a navy.”
Other dialects, such as Black English or Irish English are often looked at as bad English—not only by teachers, but also, often, by the people who speak those dialects. This is a big problem with prescriptive grammar; it contributes to discrimination against people who were not born into families speaking the standardized language, the dialect of money, power, and social status.
From a scientific point of view, all varieties of language—all dialects—are equally “correct” and require equal intelligence. They simply show different patterns. If you study it scientifically, you will discover that Black English is not made of errors. It follows rules just as much as standard English, just different rules. More surprisingly, Black English sometimes follows the rules of standard English better than standard English, yet people think it’s wrong. For example, what is the correct way to form yes/no questions in English? Look at the following pairs:
Statement: I like pizza.
Question: Do you like pizza?
Statement: She swims every day.
Question: Does she swim every day?
This shows the standard pattern for asking yes/no questions in English. Now, consider the following:
Statement: You are a teacher.
Standard English question: Are you a teacher?
Black English question: Do you be a teacher?
Wait! What? Yes, the Black English question is more correct than the standard English question. In standard English we ask yes/no questions using “do”—unless the verb is be. If the verb is be, we follow a very old pattern. Long ago, all English yes/no questions followed this pattern:
Are you a teacher?
Swim you every day?
Like you pizza?
But, not anymore! And in British English, which is more conservative than American English, we can still do this with the verb to have:
American English: Do you have the time?
British English: Have you the time?
The point is that Black American English follows the modern rule better than “correct” English, yet if people say “Do you be the teacher?”, other people will think you are speaking (or writing) wrong. This is the difference between descriptive and prescriptive grammar. Descriptive grammar tells us that Black English uses one rule for making yes/no questions, while standard English uses two rules. prescriptive grammar tells us that Black English speakers are making grammatical errors, but descriptive grammar tells us this cannot be true based on the way language actually works.
As stated before, prescriptive grammar rules are really social rules—similar to the rules for wearing clothes and using forks. Rules that we must follow so that people will not judge us negatively. And that is their purpose—to show that a person belongs to the educated class of people. Granted, the mastery of prescriptive grammar is a key to professional success. But it is not the true grammar; the true grammar can only be learned by observing and describing patterns—by creating a descriptive grammar.