There are several good handbooks on grammar and mechanics available. A reasonable online handbook (free of charge) can be found at the Grammarly blog. It provides basic information on grammar, mechanics, sentence structure, and usage. Dartmouth College’s Program in Rhetoric and Writing has identified the twenty most common errors, listed below according to the frequency with which they appear. Fuller descriptions of these and other grammatical errors can be found in Jack Lynch’s Guide to Grammar and Style.
Twenty Most Common Errors
1. Missing comma after introductory phrase
For example: After the devastation of the siege of Leningrad the Soviets were left with the task of rebuilding their population as well as their city. (A comma should be placed after “Leningrad”.)
2. Vague pronoun reference
For example: The boy and his father knew that he was in trouble. (Who is in trouble? The boy? His father? Some other person?)
3. Missing comma in compound sentence
For example: Wordsworth spent a good deal of time in the Lake District with his sister Dorothy and the two of them were rarely apart. (Comma should be placed before the “and”.)
4. Wrong word
This speaks for itself, but writers may fail to distinguish between “there” and “their” or may say that someone “imagines” something, when they meant to say that someone “envisions” something.
5. No comma in nonrestrictive clauses
Here you need to distinguish between a restrictive relative clause and a nonrestrictive relative clause. Consider the sentence, “My brother in the red shirt likes ice cream.” If you have two brothers, then the information about the shirt is restrictive, in that it is necessary to defining which brother likes ice cream. Because they are essential to identifying the noun, restrictive clauses use no commas. However, if you have one brother, then the information about the shirt is not necessary to identifying your brother. It is non-restrictive and, therefore, requires commas: “My brother, in the red shirt, likes ice cream.”
6. Wrong/missing inflected ends
“Inflected ends” refers to a category of grammatical errors that you might know individually by other names—subject-verb agreement, who/whom confusion, and so on. The term “inflected ends” refers to something you already understand: adding a letter or syllable to the end of a word changes its grammatical function in the sentence. For example, adding “ed” to a verb shifts that verb from present to past tense. Adding an “s” to a noun makes that noun plural. A common mistake involving wrong or missing inflected ends is in the usage of who/whom. “Who” is a pronoun with a subjective case; “whom” is a pronoun with an objective case. We say, “Who is the speaker of the day?” because “who” in this case refers to the subject of the sentence. But we say, “To whom am I speaking?” because, here, the pronoun is an object of the preposition “to”.
7. Wrong/missing preposition
Occasionally prepositions will throw you. Consider, for example, which is better: “different from,” or “different than?” Though both are used widely, “different from” is considered grammatically correct. The same debate surrounds the words “toward” and “towards.” Though both are used, “toward” is preferred in writing. When in doubt, check a handbook.
8. Comma splice
A comma splice occurs when two independent clauses are joined only with a comma. For example: “Picasso was profoundly affected by the war in Spain, it led to the painting of great masterpieces like Guernica.” A comma splice also occurs when a comma is used to divide a subject from its verb. For example: “The young Picasso felt stifled in art school in Spain, and wanted to leave.” (The subject “Picasso” is separated from one of its verbs “wanted.” There should be no comma in this sentence.
9. Possessive apostrophe error
Sometimes apostrophes are incorrectly left out; other times, they are incorrectly put in (her’s, their’s, etc.)
10. Tense shift
Be careful top stay in a consistent tense. Too often students move from past to present tense without good reason. Note that analyses of texts and other cultural products are kept in present tense: “Faulkner offers us clues to his characters’ motives.”)
11. Unnecessary shift in person
Don’t shift from “I” to “we” or from “one” to “you” unless you have a rationale for doing so.
12. Sentence fragment
Silly things, to be avoided. Unless, like here, you are using them to achieve a certain effect. Remember: sentences traditionally have subjects and verbs. Don’t violate this convention carelessly.
13. Wrong tense or verb form
Though students generally understand how to build tenses, sometimes they use the wrong tense, saying, for example, “In the evenings, I like to lay on the couch and watch TV.” “Lay” in thise instance is the past tense of the verb, “to lie.” The sentence should read: “In the evenings, I like to lie on the couch and watch TV.” (Note that “to lay” is a separate verb meaning “to place in a certain position.”)
14. Subject-verb agreement
This gets tricky when you are using collective nouns or pronouns and you think of them as plural nouns: “The committee wants [not want] a resolution to the problem.” Mistakes like this also occur when your verb is far from your subject. For example, “The media, who has all the power in this nation and abuses it consistently, uses its influence for ill more often than good.” (Note that media is an “it,” not a “they.” The verbs are chosen accordingly).
15. Missing comma in a series
Whenever you list things, use a comma. You’ll find a difference of opinion as to whether the next-to-last noun (the noun before the”and”) requires a comma. This is called the Oxford comma:(“Apples, oranges, pears, and banannas. . .”). Our advice is to use the comma because sometimes your list includes pairs of things; “For Christmas, she wanted books and tapes, peace and love, and for all the world to be happy.” If you are in the habit of using a comma before the “and,” you’ll avoid confusion in sentences like this one.
16. Pronoun agreement error
Many students have a problem with pronoun agreement. They will write a sentence like “Everyone is entitled to their opinion.” The problem is, “everyone” is a singular pronoun. You will have to use “his” or “her” or “his/her.”
17. Unnecessary commas with restrictive clauses
See the explanation for number five, above.
18. Run-on, fused sentence
Run-on sentences are sentences that run on forever, they are sentences that ought to have been two or even three sentences but the writer didn’t stop to sort them out, leaving the reader feeling exhausted by the sentence’s end which is too long in coming. (You get the picture.) Fused sentences occur when two independent clauses are put together without a comma, semi-colon, or conjuction. For example: “Researchers investigated several possible vaccines for the virus then settled on one.”
19. Dangling, misplaced modifier
Modifiers are any adjectives, adverbs, phrases, or clauses that a writer uses to elaborate on something. Modifers, when used wisely, enhance your writing. But if they are not well-considered—or if they are put in the wrong places in your sentences—the results can be less than eloquent. Consider, for example, this sentence: “The professor wrote a paper on sexual harassment in his office.” Is the sexual harassment going on in the professor’s office? Or is his office the place where the professor is writing? One hopes that the latter is true. If it is, then the original sentence contains a misplaced modifier and should be re-written accordingly: “In his office, the professor wrote a paper on sexual harassment.” Always put your modifiers next to the nouns they modify.
20. It/its error
“Its” is a possessive pronoun. “It’s” is a contraction for “it is.”
To learn several strategies about proofreading, please watch the short video found on this page about proofreading produced by the The Writing Center at the University of North Carolina-Chapel Hill: