We all make mistakes, but there are some that writers should never make. Though the casual tone of blogging has allowed us to be less formal with the written word, it doesn’t mean we can simply ignore the fundamental rules of writing and grammar. The occasional typo can be brushed off as an innocent oversight, but there are some writing errors that are just plain unforgivable. These blunders can ruin your credibility as a writer. 1. Fewer versus less Unforgivable: There are less days in February than in March. Correct: There are fewer days in February than in March. Use fewer when referring to things that can be counted. For example, “She ate fewer cupcakes tonight than she did last night.” Use less when referring to volumes or to things that cannot be counted: “The cupcakes had less frosting yesterday.” 2. Affect versus effect Unforgivable: Our services will have a positive affect on your business. Correct: Our services will have a positive effect on your business. Although affect and effect can each be used as either a noun or a verb, the more common usages are affect as a verb and effect as a noun. In the example above, the effect is the result of the services. In the sentence, “Our services can affect how customers see your business,” affect is to produce an effect upon, or to influence. 3. Pronoun/antecedent disagreement Unforgivable: If you hire a professional copywriter, make sure they know how to write. Correct: If you hire a professional copywriter, make sure she knows how to write. In the above sentences, copywriter is singular. So the pronoun should be singular, as well. Many people avoid gender-specific pronouns, but all too often, that just leads to bad grammar. The correct choices include using “he or she”—pick one and stick to that gender—or using a plural antecedent (which is the noun to which the pronoun refers): “When hiring copywriters, make sure they know how to write.” 4. Misspellings Unforgivable: Are you on Goggle+? Correct: Are you on Google+? Be sure to proofread your work. Misspelling the name of a company, a website or a person is a sign of sheer laziness. 5. It’s versus its Unforgivable: The pizza became famous for it’s unique flavors and toppings. Correct: The pizza became famous for its unique flavors and toppings. This is a common mistake because technically, it’s follows the rule of using an apostrophe to convey possessives (for example, the pizza’s flavor). But an apostrophe is used for the contraction of it is or it has: “It’s the best pizza ever!” 6. Misuse of the semicolon Unforgivable: I love to write; but I hate using semicolons. Correct: I love to write; I hate using semicolons. Semicolons can get confusing. Rather than make an unforgivable mistake, I tend to avoid them whenever possible. Use a semicolon to connect two related independent clauses without a conjunction (the example above), or within a complex series: “I’ve lived in Waukegan, Ill.; Alameda, Calif.; and Bartlett, Tenn.” Do not use a semicolon with a conjunction (and, but, for, or, so, nor, yet). 7. Alot versus a lot Unforgivable: Alot of people make this mistake. Correct: A lot of people make this mistake. Alot is not a word! 8. Inconsistency Unforgivable: His favorite colors are red, blue, and green. My favorite colors are yellow, purple and pink. Correct: His favorite colors are red, blue and green. My favorite colors are yellow, purple and pink. Each of the above sentences is structurally fine, but the top two are inconsistent with each other, because the first sentence uses the Oxford comma and the second does not. Don’t use the Oxford comma in one sentence and leave it out the next. Don’t spell out ten in the first paragraph and write 10 in the last. Writing rules change depending on what style of writing you follow (Chicago Manual or Associated Press), but whichever style you use, be consistent throughout your copy. 9. Poorly cited stats and quotes Unforgivable: Women make up 97 percent of Pinterest users. Correct: According to AppData, women make up 97 percent of Pinterest users. Back up statistics and quotes by letting your readers know where you got the information. If you can, provide a link back to the exact Web page where you found the data. Failure to prove where you got your facts will weaken your content. 10. Then versus than Unforgivable: I enjoy sitting much better then running. Correct: I enjoy sitting much better than running. Than is used for comparisons, although then is used to refer to a point in time or “in addition to.” For example: “Back then, I was strong enough to run a marathon. Now, my legs and lungs are in worse shape than they used to be.” 11. Lose versus Loose Unforgivable: If you loose your keys again, I’m not letting you in. Correct: If you lose your keys again, I’m not letting you in. Lose is a verb, and loose is most commonly used as an adjective. Use loose when referring to something that doesn’t fit or isn’t secure, such as loose pants or loose attachments. Loose can also be used as a verb—for example, “loose a knot”—but in these cases, loosen is a more common word. 12. Stolen content Unforgivable: Always. Correct: Never. This one isn’t really a mistake, but rather just plain wrong. Never steal and use content that isn’t yours and play it off as your own work. Not only is that theft, but it’s also copyright infringement. Write original, informative content, and always proofread your work. Any common writing mistakes that you think are simply unforgivable? Jacqui MacKenzie is a writer for Straight North, an Internet marketing Chicago firm that provides social media services, SEO, and more. A version of this story first appeared on the 12 Most blog. This story first ran on PR Daily in April 2012.