- Sentence fragments: A sentence fragment is not a complete sentence; it is only part of one and cannot express a complete thought on its own. Fragments occur when one or both of the two essential parts of sentence, a subject and/or verb, are missing; they also occur when a dependent or subordinate clause is treated as an independent clause.
- Fused or run-on sentences: Fused sentences occur when two or more independent clauses (complete thoughts) have no punctuation separating them. To correct the error, divide them into separate sentences with a comma and appropriate coordinating conjunction showing their relationship (and, but, or, nor, so, yet), a semicolon, or a period. Also, you can turn one sentence into a dependent clause to show its particular relationship with the independent clause.
- Missing comma in a compound sentence: A compound sentence is made up of two or more independent clauses, and these clauses must be connected by a comma followed by a coordinating conjunction (and, but, or, nor, so, yet) that clarifies the relationship between the independent clauses.
- Comma splice: A comma splice occurs when two independent clauses are connected by only a comma or by a comma(s) plus a conjunctive adverb or transitional phrase (therefore, however, for example). To correct the error, use a comma plus coordinating conjunction (and, but, or, nor, so, yet), a semicolon, a semicolon plus conjunctive adverb followed by a comma or a period to create two sentences.
- Missing comma after an introductory element: Introductory words, phrases, or clauses are set off from the rest of the sentence by a comma. When there is no chance of misreading, the comma can be omitted after very short phrases.
- Missing comma(s) with a nonrestrictive element: A nonrestrictive element is a word, phrase, or clause that gives additional or optional information. This information is not essential to the meaning of the sentence and can be omitted. When such elements are embedded in a sentence, they are set off by a pair of commas; when they come at the beginning or end of the sentence, they are set off by a single comma.
- Unnecessary comma(s) with a restrictive element: A restrictive element is a word, phrase, or clause that is essential to the meaning of the sentence; if it is deleted, the meaning of the sentence will change. A comma should not set off important or restricted information.
- Missing comma in a series: A series consists of three or more parallel words, phrases, or clauses that appear consecutively in a sentence. Traditionally, all items in a series are separated by commas; however, some newspapers, magazines, and other professional media leave out the final comma before the and or or. Whichever style you choose, be consistent.
- Missing or misplaced possessive apostrophe: Use an –‘s or an –s’ or an –s’s to show a noun is possessive. If the noun does not end in an –s or is an indefinite pronoun (anybody, everybody, something), add an –‘s; if the noun is singular and has an –s ending, add –‘s. If the noun is plural and ends in –s, use only the apostrophe.
- Wrong or missing verb endings: Although they are sometimes dropped in speech, the verb endings –s or –es and –ed or –d are important markers of standard English and must be used in writing. Problems occur with the required –s ending for a third-person singular verb in the present tense (he runs, she jumps, I run, they jump).
- Wrong verb form: Although some English dialects drop verb endings, written English requires the use of standard verb forms. Problems occur when forming tenses, such as the progressive or perfect tense, with the past-tense and past-participle forms of irregular verbs.
- Unnecessary shift in tense: As verb tense establishes the time of the actions being described, it is very confusing for the reader when the writer shifts tenses in a passage, such as from past to present tense in a description about something that happened in the past. However, literary convention requires the present tense when describing fictional events.
- Lack of agreement between subject and verb: In standard English verbs must agree with their subjects in number (singular or plural) and in person (first, second, third). Knowing the rules of agreement, being able to identify each subject, and recognizing the number of each subject are critical in managing agreement correctly. The present tense is where most errors occur: some result from dialects that drop –s endings off third-person singular verbs (he run instead of he runs); others happen when the verb agrees with another noun coming between it and the subject. Yet others occur with the irregular verb be or the verbs have and do, sentences beginning with There or Here, which result in the subject following the verb, and the indefinite pronouns (everyone, everybody, nobody, etc.) most of which are singular.
- Vague pronoun reference: A pronoun should refer clearly to a specific antecedent. Pronouns like he, she, it, they, this, that, or which stand in for a noun or noun phrase already named or about to be named. When the pronoun’s reference is vague, readers are unable to tell for sure whom or what the pronoun is referring to and will be confused. These errors often occur when there is a lack of specificity and the pronoun could refer to more than one noun; they also occur when the writer tries to make a pronoun refer to an entire clause or sentence.
- Lack of agreement between pronoun and antecedent: Pronouns stand in for a specific noun or noun phrase (the antecedent) and must agree in number, gender, and case. Errors commonly occur with indefinite pronouns (each, anyone, everything) that do not refer to particular persons or things. Some indefinite pronouns (all, any, enough, more, most, none, some) can be singular or plural depending on the context; however, most of the indefinite pronouns are singular while a few (some, both, many, others, ones, several) are always plural.