Introduction
This time around, I will be talking about basic grammar rules that writers should abide by. However, I am going to discuss only American grammar rules. If you are using British, Singaporean, Australian, or any other form of English, these rules may or may not apply to you. Some of them are common for all forms of English, and some of them can get a little ambiguous. From now on, I will assume that anyone reading this writes in American English.



1) Subject-Verb Agreement
Subject-verb agreement is one of the most fundamental rules of grammar. I think most of us know this rule; some of us just forget about it from time to time. It basically goes down to:

a) If the subject of your sentence is or can be replaced by I, you, we, or they, then the verb should be in its base form.

b) If the subject of your sentence is or can be replaced by he, she, or it, then the verb should end with an "s" or "es."

Of course, this applies to words in their present form. For other tenses, verbs don't change their forms. The exception is be, which changes to was and were, depending on the subject. This is very basic grammar; all of us should already know this. Just reminding you :)



2) Tense-shifting
This is one of the most common mistakes writers make. I've already explained this a little in the "Basic Writing Guide," but I'll talk about it again: do not go between two tenses in your narration for no reason. If you choose to use past tense for narration, stick with it. If you choose present tense, stick with it. If you choose future tense... well, good luck. But stick with it, too.

So, what's wrong with this sentence?

I don't know what he did, but he definitely did something. His eyes told me so.

It should be: "I didn't know what he'd done, but he had definitely done something. His eyes told me so."

Or: "I don't know what he's done, but he's definitely done something. His eyes tell me so."



3) Run-on Sentences
This is probably the most commonly made mistake. Everyone has written a run-on, myself included. I still write run-ons from time to time, when I'm not really focused on not making them. So, what is a run-on?

A run-on sentence is any sentence that is not properly punctuated. Most often, writers make run-ons because they fail to use commas correctly. The comma rules are pretty complex, so I won't get into too much detail with them. You can always check a grammar book or go online to look up the exact rules! I will only give an overview of the most important rules that will eliminate most of your mistakes.

a) Two independent clauses joined together with a conjunction should ALWAYS be separated by a comma. For example: I ate lunch, and I went to work. Notice the comma. Because I ate lunch and I went to work are two separate ideas that make perfect sense alone, they must be separated by a comma even when joined with the conjunction and. Be careful--words like because change the independent clause into a dependent clause!

b) An independend clause joined with a dependent clause does NOT have a comma separating the two parts. For example: I ate lunch and went to work. There is no comma here, because went to work is not an independent sentence, as it does not have a subject. Another example: I like K-Pop because it is addictive. Even though it is addictive is an independent clause, the word because changed it into a dependent clause(because it is addictive cannot stand alone--because it is addictive what?). Therefore, there is no comma used.

c) Two independent clauses joined together without a conjunction should ALWAYS be separated by a semi-colon. For example: I like K-Pop; it is addictive. There is no conjunction or marker word connecting them, so there has to be a semi-colon. Another example: I called Jane; however, she didn't pick up. Here, you might be a little confused, but let me help you. The sentence however, she didn't pick up can stand alone, as an independent clause. Technically, you should not use words like and or but the same way I used however above. But most people do it anyway. That's what makes most non-native speakers so confused; it's hard to differentiate between real conjunctions and independent markers...

d) Lists of more than 2 items should always have commas everywhere. Example: I bought an apple, an orange, and a banana. A lot of people miss the last comma before and, but that's an error. You only don't put the comma if the list is of two items, like in I bought an apple and a banana.

e) Use a comma before which, who, or that only when the information is parenthetical. This means that if the information you're providing is not a defining feature of whatever you're talking about, use a comma. Here's an example: I met Laura, who found my dog. This sentence means I met Laura, who, by the way, found my dog. She's Laura, and she happened to find my dog, and I'm just telling you because I feel like. While if I say I met Laura who found my dog, it means that this is THE Laura that found my dog. In case you were not sure which Laura I was talking about.

There are many more rules, but these are the ones that are most often violated. Feel free to ask Google for more help on commas should you need it. Or, if you can't find an answer on Google, I'll try to help you the best I can.



4) Quotations and Punctuation
Another thing I often see done wrong is punctuation before/after quotations. It's not really that difficult once you get used to it. First of all, do NOT put punctuation behind your quotation mark. That's an error. Here are common errors I've seen:

"He is fine". -> should be "He is fine."
"He is fine,". -> should be "He is fine."

Second thing that often gets messed up is case of the sentence that follows the direct speech quote. This is how it always should be:

"Hello," he said.
"Hello!" he said.
"Hello?" he said.
"Hello." His greet sounded insincere. -> A period is often used when there is no inquit (a form of "he says") following it, but rather a full independent sentence.
He said, "Hello." -> A comma is strongly preferred in cases like this one.
"Hello," he said. "How are you?"
"Hello," he said, "how are you?" -> The difference is the same as in "Hello. How are you?" and "Hello, how are you?"



5) Pronouns
The last topic of the day concerns pronouns. People make all sorts of mistakes with pronouns, but they don't even realize it. Here are a couple of errors that I see very frequently:

a) Which vs. That - this mistake can be easily avoided. You cannot have that after a comma--this means, you cannot use that to introduce extra information. Any sentence with that should be of vital importance to the noun it refers to. Also, you should not use the word that to refer to people. It's not really wrong, but in academic writing and on SATs, it apparently is.

b) Who vs. Whom - this error is likewise very easily avoidable. Just remember that who refers to a subject, and whom refers to an object. Surprisingly, most people make a mistake of saying who do you love instead of whom do you love, which is grammatically correct.

c) Unclear reference - don't use too many hes or shes. Example: John went to see Mark. He broke his ankle, so he wanted to say hi. This is an extreme, but now you see clearly what is wrong. Which he refers to whom?

d) You're vs. Your, It's vs. Its, They're vs. Their, etc. - mistakes of this sort are really silly. If it has an apostrophe, it's a shortening of the pronoun + to be. If it does not, it is a pronoun. Easy as that.

Yay, you've made it! Now, if you remember all of this, you should make very few grammar errors! Of course, there are many, many more to discuss, like particle usage, prepositions, verb forms, dangling participles, etc. But that would take forever to explain well, and I believe your English teachers get paid for that job ;)



Other guides: Basic Writing Guide, Publicity Guide