Six grammar rules cause more trouble than most: the semicolon, the -ed ending of the past tense, the subjunctive (if I were), there, their, and they're, the comma, and the choice between which and that. This article explains each rule with examples.
Autocorrect and spell checkers catch many mistakes, but not all of them, and some rules confuse even native speakers. So these are the 6 grammar rules to know and follow.
1. The semicolon
A simple way to look at a semicolon is as a period on top of a comma. Like a comma, it marks a pause, but a slightly longer one. Many people find the semicolon difficult because they use it too often or in the wrong place. It has two main uses.
First, a semicolon joins two complete clauses that belong together. A complete (independent) clause has a subject and a verb and could stand on its own as a sentence:
No matter what you decide to write about, make your own decisions; as a result, others will love your work.
Please call me later; you can let me know how you feel then.
Second, a semicolon separates the items of a list when the items already contain commas:
The tour stops in Paris, France; Rome, Italy; and Vienna, Austria.
How to use a semicolon explains both uses in more detail.
2. Adding -ed to verbs
To talk about the past, add -ed to a regular verb: walk becomes walked. The same form is also the past participle, as in I have walked. Irregular verbs follow their own patterns and are trickier. Drink, for example, does not take -ed: its past tense is drank, not drinked.
Watch the spelling when you add an ending. A one-syllable verb that ends in a single vowel and a single consonant doubles the consonant (but never the letters w, x, or y), and so does a longer verb that is stressed on its last syllable. A verb that is stressed on an earlier syllable does not:
| Verb | Past tense | Present participle |
|---|---|---|
| stop | stopped | stopping |
| admit | admitted | admitting |
| target | targeted | targeting |
For the irregular verbs, read irregular verbs: the past tense of catch, bring, and more.
3. The subjunctive
The subjunctive is a verb form for things that are not real: wishes, imagined situations, and things that are contrary to fact. When you write about a situation that is not true, was becomes were. This usually happens after if or wish:
- Avoid in formal writing: If I was a very famous person
- Correct: If I were a very famous person
- Avoid in formal writing: I wish I was ten feet tall.
- Correct: I wish I were ten feet tall.
Keep one exception in mind. When if means whether, for example in a reported question, the sentence is not about an imagined situation, so it does not take the subjunctive:
- Wrong: The girl asked the police officer if he were happy with his job.
- Correct: The girl asked the police officer if he was happy with his job.
4. There, their, and they're
Few words cause as many problems as there, their, and they're, because they all sound the same. Yet each one has its own job:
- They're is a contraction of they are. If you read it as two words, you are unlikely to use it wrongly. In formal writing, it is best to write they are in full.
- There refers to a place, like here.
- Their shows possession, just like my, your, its, our, his, and her.
They're always trying to park their car there.
There, their, and they're has more examples.
5. The comma
Use a comma before a conjunction such as and, but, or so when it joins two complete sentences into one:
Peter likes to shop, but he never spends more than a hundred dollars.
Commas also separate three or more items in a series. Put one before the last item too (the Oxford comma), which often prevents a misreading:
I love taking my new car, my kids, and my dog out for a drive.
Do not join two sentences with only a comma and a word like however, though. That is a comma splice. Use a semicolon or a period instead:
- Wrong: Peter likes to shop, however, he never spends more than a hundred dollars.
- Correct: Peter likes to shop; however, he never spends more than a hundred dollars.
6. Which, that, and witch
"Which witch is that witch you're with?" Witch and which sound alike and are spelled almost the same, but the pair that people really confuse is which and that. Both can introduce a relative clause, a part of the sentence that describes a noun. The difference is whether the reader needs the clause to know which thing you mean:
- Use that, without commas, when the clause identifies the noun. Without it, the reader would not know which one you mean.
- Use which, between commas, when the clause only adds information. You could leave it out, and the sentence would still point to the same thing.
The car that has the red lining needs painting. (You have several cars, and this one needs paint.)
Our car, which is blue with a red lining, needs painting. (You have one car, and the clause only describes it.)
This rule is strict in American English. In British English, which often introduces an identifying clause too, but a clause that only adds information always takes which and commas.
Witch and which are easier to keep apart:
- A witch is a person who is believed to have magic powers, like the Wicked Witch of the West in The Wizard of Oz. Never call a witch a "which", or she might cast a spell on you.
- Which is a question word (Which one do you want?) and a relative pronoun that refers to a thing, as in the examples above.
For more pairs like these, read commonly misused words.
Practice makes perfect
Remembering all of these rules is not easy, but the more often you apply a rule, the easier it becomes. The Spell Checker checks grammar and punctuation as well as spelling, so it can flag mistakes like these while you learn the rules.