Imagine that you're a little old lady living alone in a cabin way out in the woods. You've been bothered lately by howling you've heard late at night. That's not on your mind right now, though, because your granddaughter is on her way to see you.
She's bringing a picnic basket, so the two of you can have a nice lunch together. You're anxious for her to arrive. To pass the time, you open up the cabin windows and tidy up a bit.
Suddenly you hear sounds coming through both the front and back windows simultaneously:
Front window: "Let's eat, Grandma!"
Back window: "Let's eat Grandma!"
Those of you reading this might have already guessed that it's Little Red Riding Hood at the front window and the Big Bad Wolf at the back window. We won't spoil the end of the story if you're not familiar with it, but it serves to highlight the importance of grammar.
If you're currently being tasked with memorizing subject and object pronouns, then you may be WONDERing who invented grammar and why do you need to study it anyway. As Grandma in our story would tell you, though, grammar can be a matter of life or death! In her case, that one little comma was the difference between a nice picnic with her granddaughter and being eaten by a wolf!
There are many different definitions of exactly what constitutes grammar. Many grammar experts think of it as the rules, systems, structures, and even science of language and its proper use.
Grammar can include many different aspects of language, from spelling to punctuation. When most people discuss grammar, they're usually talking about accidence, orthography, and syntax.
Accidence concerns changes in words to change their meaning. Examples would include tenses (past, present, and future: went, go, and will go), numbers (singular and plural: goose and geese), and pronouns (subject and object pronouns: I vs. me).
Orthography concerns writing words correctly with the proper letters per standard usage. Misspelled words and words with erroneous or misplaced apostrophes, for example, would be orthographical errors.
Syntax concerns the proper arrangement of words to form meaningful sentences. "Scared of the wolf, the picnic was not enjoyable" would be an example of a sentence with poor syntax, since the picnic was not scared of the wolf!
Rules of grammar have developed for every language over time. Most of them developed long ago when a language was first written down.