accept/except: Accept means “to receive willingly” or “to regard as proper.” Except means “excluding.” Probably the easiest way to keep these two words straight is to think of the word acceptable; it applies to something that is satisfactory or adequate, in other words, something you would accept: “The work was acceptable.” There is no equivalent word exceptable.

affect/effect: The word affect is almost always used as a verb (an action word) that means “to influence.” For example, “Her proposal will affect our bottom line.” It is used as a noun (meaning “emotion”) only in the context of psychology or psychiatry: “The patient has a flat affect.” In contrast, effect is almost always used as a noun that means “result.” For example, “The new incentives had a positive effect.” It is used as a verb only to mean “to initiate” or “to bring about”: “We will effect change throughout the system.”

apostrophe: Most grammar books and style guides have at least two or three pages devoted to apostrophe-related rules, but the most important ones to remember are these:

• When you are adding an s to a word simply to make it plural, don’t use an apostrophe: “The contract packet will go out in the mail today.”/”The contract packets will go out in the mail today.”
• To indicate possession with a singular noun—even one that ends in s—add the apostrophe and s: “The report must be on Russ’s desk in the morning.”
• To indicate possession with a plural noun, add only the apostrophe in most cases: “The three products’ features are unequal.” The exception to this rule is for nouns that have irregular plurals (i.e., plurals formed in some way other than by adding an s to the word, such as women or children). In these cases, the nouns are treated as if they were singular: “The women’s study group will meet on Thursday.”

If you run into a problem with a plural possessive (the third rule above), you can sometimes adjust your sentence to avoid the problem altogether: “The features of the three products are unequal” or “The study group for women will meet on Thursday.”

assure/ensure/insure: These three words all have the general meaning “to make sure,” but they are used in different situations, as follows: Assure is used only when you are putting someone’s mind at ease (“I assure you, Mr. Smith, that we will complete the project on time”). Insure is used only in the context of the insurance you buy to protect your property, protect yourself against medical expenses, and so on (“We need to insure the corporate helicopter”). Ensure is used in other situations to guarantee a condition or event (“Our quality control system ensures that our products are free of defects”).

definitely: Many people want to spell this word “definately.” Try to remember that the last part of the word is spelled the same way as “nightly” is often spelled in a red-light district: “Dancing Girls Nitely!”

e.g./i.e.: The abbreviation e.g. means “for example.” The abbreviation i.e. means “that is”; you use i.e. when you want to repeat something you’ve stated in different words. For example: “The proposal was unacceptable; i.e., it did not address the requirements of the solicitation.” One way to differentiate between the two abbreviations is to think of the nonsense phrase “For example, eggs,” which may remind you to use e.g. when giving an example. Both abbreviations require a comma after the second period.

he/she/they: The English language does not offer good options for writing about a single person of unknown gender. For example, if you start out writing about “the user,” what do you do when you later want to refer to that person as he or she? Many writers choose they, which is incorrect because they refers to more than one person. One simple solution is to make the subject plural from the beginning. Instead of writing “the user,” write “users,” and you can refer to them with the plural pronoun they throughout your text.

I/me: Remember what your mother used to say when you said, “John and me are going over to Frank’s house”? Chances are, she’d respond with “John and I.” You can always tell whether you should use I or me in this type of sentence by simply eliminating the other person. You wouldn’t say, “Me is going over to Frank’s house,” so you know that your mother was right; the correct phrasing here is “John and I are going over to Frank’s house.”

it’s/its: The word it’s (with the apostrophe) is a contraction (don’t, I’m) and, like other contractions, is a combination of two words (do not, I am); in this case, the contraction means “it is”: “It’s going to be difficult to meet the deadline.” The word its (without the apostrophe) is a possessive pronoun that means “belonging to it”: “The firm is changing its hiring practices.”

their/they’re/there: The word their means “belonging to them”: “Their departments will be merging.” The word they’re is a contraction of they are, and that’s what it means: “They’re going to Florida next week.” The word there has multiple uses, but it most commonly refers to a place (“over there”) or is used to introduce a sentence (“There is much to be done”).

who/whom: The test to determine whether a sentence requires who or whom is to turn it into a question and see whether he or him fits as an answer. If the answer would be him, then whom is the correct choice. Because both words end in m, the connection should be easy to remember. Consider this sentence: “He is the manager [who/whom] we have selected to lead the project.” As a question, the sentence becomes: “[Who/Whom] have you selected to lead the project?” And the answer would be “We have selected him.” Thus, you know that whom would be the correct choice in the original sentence.

you’re/your: You’re means “you are”: “You’re going to work with Jill’s group on this project.” Your means “belonging to you”: “Your proposal is being discussed by upper management.”