Grammar has long been a subject of study—as a companion to rhetoric in ancient Greece and Rome, as one of the seven liberal arts in medieval education. Although the methods of studying grammar have changed dramatically in recent times, the reasons for studying grammar have remained essentially the same.
One of the most sensible answers to the question of why grammar matters appears in a position statement on the teaching of grammar in American schools. Published by the National Council of Teachers of English (NCTE), the report is refreshingly free of educational cant. Here's how it begins:
Grammar is important because it is the language that makes it possible for us to talk about language. Grammar names the types of words and word groups that make up sentences not only in English but in any language. As human beings, we can put sentences together even as children—we can all do grammar. But to be able to talk about how sentences are built, about the types of words and word groups that make up sentences—that is knowing about grammar. And knowing about grammar offers a window into the human mind and into our amazingly complex mental capacity.
People associate grammar with errors and correctness. But knowing about grammar also helps us understand what makes sentences and paragraphs clear and interesting and precise. Grammar can be part of literature discussions, when we and our students closely read the sentences in poetry and stories. And knowing about grammar means finding out that all languages and all dialects follow grammatical patterns.
(Brock Haussamen, "Guideline on Some Questions and Answers About Grammar", 2002)
The author of this introduction, Brock Haussamen, is professor emeritus of English at Raritan Valley Community College of New Jersey. Whether or not you teach English for a living, the full report, "Guideline on Some Questions and Answers About Grammar," is well worth the read for anyone interested in English grammar.*
Additional Perspectives on Grammar
Consider these explanations of why grammar matters from other experts in English and education:
on the utility and importance of the study of Grammar, and the principles of composition, much might be advanced, for the encouragement of persons in early life to apply themselves to this branch of learning... It may indeed be justly asserted, that many of the differences in opinion amongst men, with the disputes, contentions, and alienations of heart, which have too often proceeded from such differences, have been occasioned by a want of proper skill in the connexion and meaning of words, and by a tenacious misapplication of language."
(Lindley Murray, English Grammar, Adapted to the Different Classes of Learners, 1818)
"We study grammar because a knowledge of sentence structure is an aid in the interpretation of literature; because continual dealing with sentences influences the student to form better sentences in his own composition; and because grammar is the best subject in our course of study for the development of reasoning power."
(William Frank Webster, The Teaching of English Grammar. Houghton, 1905)
"The study of language is a part of general knowledge. We study the complex working of the human body to understand ourselves; the same reason should attract us to studying the marvelous complexity of human language...
"If you understand the nature of language, you will realize the ground for your linguistic prejudices and perhaps moderate them; you will also more clearly assess linguistic issues of public concern, such as worries about the state of the language or what to do about the teaching of immigrants. Studying the English language has a more obvious practical application: it can help you to use the language more effectively."
(Sidney Greenbaum and Gerald Nelson, An Introduction to English Grammar, 2nd ed. Longman, 2002)
"Grammar is the study of how sentences mean. And that is why it helps. If we want to understand the meaning conveyed by sentences, and to develop our ability to express and respond to this meaning, then the more we know about grammar, the better we will be able to carry out these tasks...
"Grammar is the structural foundation of our ability to express ourselves. The more we are aware of how it works, the more we can monitor the meaning and effectiveness of the way we and others use language. It can help foster precision, detect ambiguity, and exploit the richness of ｅxpression available in English. And it can help everyone—not only teachers of English, but teachers of anything, for all teaching is ultimately a matter of getting to grips with meaning."
(David Crystal, Making Sense of Grammar. Longman, 2004)
"[T]he study of your own grammatical system can be quite revealing and useful, and provides you with insights into how language, your own and others', whether spoken or signed, actually works...
"With an understanding of how language actually works, and a concise vocabulary to talk about it, you will be equipped to make more informed decisions and choices about grammar and usage, and to tease out linguistic fact from linguistic fiction."
(Anne Lobeck and Kristin Denham, Navigating English Grammar: A Guide to Analyzing Real Language. Wiley-Blackwell, 2013)
*Also worthwhile is the Assembly's website, simply outfitted with grammar links, teaching tips, and a grammar bibliography. In short, it's a place where people know that grammar matters—and how, and why