As a copyeditor/proofreader, I wish I had a nickel for every time I either corrected this mistake and/or re-read a sentence to verify that the right word had been used.
This explanation could takes pages and pages to clarify, but let’s just give you a simple rule to use:
If you can substitute the word “influence” in the sentence and get the same basic meaning, then use “affect.”
The threat of rain affected our plans for the day.
Now, substitute “influence”:
The threat of rain influenced our plans for the day.
The basic intent is the same; therefore “affect” is the right word.
If you can substitute words like “reaction” or consequence” in the sentence and get the same basic meaning, then use “effect.”
The effect of the rain was that we moved our backyard picnic into the kitchen.
Now, substitute “consequence”:
The consequence of the rain was that we moved our backyard picnic into the kitchen.
Well, OK, it isn’t something you would likely say, but the meaning of the sentence remained basically the same, so “effect” is the right word.
Once again, this is a very simplified rule, but you should get the general point. If you can make the substitutions.
I’ve given you without changing the basic meaning of the sentence, then you will know which word is the right word.
It’s vs. Its
This one is so easy, and yet it is often missed.
Oh, let me re-write that:
This one is so easy, and yet it’s often missed.
There’s your first clue: “it’s” is the contraction of “it is.” It’s NOT the singular possessive form of “it.” You know that if you want to indicate that the ball belongs to Bob, you write “Bob’s ball.” However, if “it” has a bad smell, then you write “its smell was awful.”
If you can substitute “it is” in the sentence, and the meaning remains unchanged, then use “it’s.”
However, the use of contractions in formal writing is not generally approved. You should not use any contractions in business communications, texts, or any writing that is formal.
There, They’re, or Their
Once again, this is easy and yet so many people miss it.
“There” indicates a place or a situation.
“They’re” is the contraction of “they are.” If you can substitute “they are” in the sentence, then use “they’re.”
“Their” is a plural possessive, that is something belongs to more than one person. If you can substitute more than one name (or thing) and not change the meaning of the sentence, then use “their.”
There are many other common grammar mistakes, but these few are certainly among the most common. If you are planning to write something, and you are unsure about some of the more basic grammar rules, I suggest you buy an easy-to-read-and-understand grammar book. Any bookstore has them, and you can buy great self-help books for under $20. I have three and I use them constantly!
Of course, your best course of action is that for anything you write for publication or business purposes, you should engage the services of a proofreader. And don’t wait until you think you are “all done” with the project! Get the proofreader involved as soon as you have a working draft.
Proofreaders are often great sources to help you unravel difficult-to-understand text and can help you achieve the best possible manuscript.