There are many different reasons to write. You might write simply for self-expression, or as a way to help clarify and work though things that are on your mind. You might write in a business setting, communicating with peers or with those higher up the ranks–or from outside a business to someone inside the business. You might write creatively, with an eye toward publication. You might write for a class, or to publish in a scholarly journal.
Each of those kinds of writing has different expectations in terms of formality of language, formatting (how the thing actually looks on the page–even if the “page” is an electronic file or email), an approach. Each one will require something slightly different from you in terms of how you approach what you write, and what you do after you first put your ideas into words.
Writing for yourself, with only yourself as the audience, is, of course, the easiest. There are zero rules or expectations; you write however pleases you.
However, as soon as you are writing with an eye toward publication–even if you are writing creatively, whether that means poetry or song lyrics or fiction or personal essay–then rules start to apply, because then you need to do everything you can to make sure the words you put together have the effect on your audience that you intend. One of the biggest mistakes my students have made in the past is to think that, because they’re writing creatively, they don’t have to worry about punctuation, or what words mean, or how sentences work.
Of course, if you read many modern poets (that is, anyone who wrote after the First World War), you’ll see poets who ignore all the rules: e e cummings comes to mind (and the fact that his name is given with lowercase letters and no periods after his initials is an indication of how firmly he rejected the rules). But in order to break the rules effectively, you first have to know what the rules are. This frequently applies to art of any kind. Even abstract painters and sculptors usually learn the rules of drawing the human figure and realistic still lifes. Yes, there are people who don’t go through the process of learning the rules and then breaking them, but those people are the exceptions. Most of us need to learn the discipline before we can play around with it effectively.
It’s also true that, if you’re well educated and you’re in a business setting, you’ll see people using the language in ways that will make you wince–and sometimes, someone will be pretty savage about the errors another person has made in a business setting. You don’t want to be the person making the mistakes.
One other truth is that the language changes, and so do the rules. Think about the way our culture is working to accept “they/them/their” as singular pronouns applying to one specific individual. In casual speech, we’ve used those words to refer to an unspecified indivual for a long time–as in “Someone forgot their coat.” It’s more awkward and potentially confusing to use those pronouns to refer to one particular person, as in “The coat belongs to the person in the pink shirt in that group over there; give it to them.” (“To … the group? Oh, wait, I get it now…”) There are some old fogeys who are still grumping about it being “wrong” to refer to a singular person with pronouns that have been considered plural–and up until very recently, I used to hammer the rule with my students that, in academic writing, “they/them/their” should only be used when referring to a plural entity. Now, of course, I wouldn’t do that. So rules change–but it still behooves us to know what the rules are, even when they’re in the process of changing.
The most rigorously structured, highly formalized form of writing is still academic writing. Again, the rules tend to change; for instance, it used to be a no-no to refer to ourselves, as if the piece had been written by a disembodied intellect with no human attached, but it’s now pretty universally accepted that we may refer to ourselves if the situation calls for it. But still, if you’re writing in an academic setting, know what is expected of you: ask your teacher or professor about what rules you’re supposed to follow, or, if you’re sending something off to be published, check with the publisher about any style rules they follow.
One final note about this topic: when you’re first writing, no matter your purpose or audience, don’t worry about any of that: just get your ideas down. Remember that thing about revising and editing that I discussed in a previous post? That applies to any form of writing you use for any audience other than yourself and your close friends and family. It’s always wise to be more formal than a situation calls for than to not be formal enough. Once you’ve got a first draft written, think carefully about your audience–and make sure what you share with them is appropriate in every way.