It was the best of sentences, it was the worst of sentences - June Casagrande 2010

The deadliest catches: The most incriminating errors and how to avoid them

Everyone makes typos. Less-experienced writers are often mortified by them, but there's no need to be. Even the most meticulous pros let a typo slip in once in a while, and the best editors and proofreaders fail to catch them all. If you misspell led as lead on occasion, no reasonable editor or Reader will think any less of you.

But there are mistakes and there are mistakes. Some are understandable. Others are code for "I'm a rank amateur."

If I see it's in place of its a single time in an article, I assume the writer made a typo. If I see it twice, that's a whole different story. That tells me—and a lot of other writers, editors, wordsmiths, and grammarphiles I know—that the writer is out of her element. She's not a pro. The grouchier among us might use words like semiliterate and hack.

So instead of agonizing over how to avoid every single typo, channel your energy into the important ones. Here is my list of iconic mistakes—ones that really do make you look bad. My selection process wasn't exactly scientific. These are just the errors that, in my experience, are most likely to inspire eye rolls and unkind thoughts about a writer's skill level.

its / it's: The possessive of it does not take an apostrophe: The dog wagged its tail. The version with the apostrophe is always a contraction of it is or it has: It's been a fun vacation.

there / their / they're: There refers to place: Put it there. Their denotes possession: Their house is the green one. They're is a contraction of they are: They're good people.

lets / let's: Without an apostrophe, this is the verb to let conjugated in the third-person singular: He lets the dog out in the morning. With an apostrophe, it is a contraction of let and us: Let's go to the park.

whose / who's: To show possession, use whose: Can you tell me whose job that is? The one with the apostrophe is a contraction of who is or who has: Who's there?

could of / would of / should of: These are always wrong. They should be could have, would have, and should have, or, less formally, could've, would've, and should've. That's because of is not a verb and therefore can't be used to form verb tenses. Modal auxiliaries like could and should can work this way with the main auxiliaries have, be, and do, but not with the preposition of.

where / wear / were: Where is a place: Where are you going? Wear means "to have on clothing": Lana and Tom wear matching shirts. Were is a past tense form of be: We were so young.

have went / have ate / other wrong participle choices: Whenever you're not sure of a correct past participle, check the main word in the dictionary. Most dictionaries list in bold the past-tense and past-participle forms of irregular verbs. Most do not list these forms for regular verbs, but some do. So, under eat you'll see something like ate, eaten in bold letters. That tells you that eat is an irregular verb, that its past tense is ate (Liam ate a sandwich), and that its past participle is eaten (In the past, he has eaten up to four sandwiches). Regular verbs like walk add -ed to form both the past tense and the past participle: Today you walk. Yesterday you walked. In the past you have walked.

accept / except: You accept a gift. When you except something, you leave it out.

compliment / complement: A flattering remark is a compliment. Something that completes something else, the way the right wine completes a meal, complements it.

affect / effect: Affect is usually a verb: That doesn't affect me. Effect is usually a noun: What will the effect of his decision be? Two rare synonyms defy this guideline. The transitive verb effect means "bring about": The candidate promised to effect positive change. The noun affect is a psychology term for emotion or a facial or bodily expression of emotion: The patient's affect was flat.

phase / faze: A phase is a stage of development. Faze is a verb meaning to upset or shock. Unfazed means unaffected.

led / lead: Led is the past tense form of the verb to lead: He led the horse to water. There is also the metal called lead, which is pronounced exactly like led.

then / than: Then is for time. Than is for comparison.

Computer's for sale / Merry Christmas from the Thompson's / other apostrophe errors: Never use an apostrophe to form a plural. It's Computers for sale and Merry Christmas from the Thompsons. Be especially careful with proper names ending in s.

grammar: Does not have an e in it.