By far, the stylistic error I encounter most frequently as a writing teacher and editor is subject/verb agreement. As you already know, you have to be sure that paired subjects and verbs "go together" grammatically. What this usually means (especially when you write in present tense) is that if a subject is singular its accompanying verb gets an "s" added to it, but if the subject is plural the verb requires no "s" (i.e., "the material ages" and "the materials age" are both correct). Simple, right? Your ear confirms the subject/verb agreement for you. For many writers, though, confusion arises when the subject and verb are distanced from each other in the sentence. Consider this incorrect example:
The material applied to the blades of wind turbines age rapidly in tests.
Do you see the problem? The word "age" should be "ages" in order to be compatible with the sentence’s subject—"the material"—but since "age" is right next to the plural "turbines" it is easy to get the sentence grammar wrong.
In a case such as this, the path to achieving perfect subject/verb agreement is to dissect the sentence mentally to determine which noun or pronoun goes with which verb. You cannot always trust your ear, especially when the word you are using is a word such as "everybody," "everyone," or "one" (all of which are singular). Also, even though "United States" or "NASA" might sound to you as though it is plural, the United States is considered to be one country, and NASA (like other organizations or corporations) is one entity (i.e., "NASA redesigned its o-rings" is correct while "NASA redesigned their o-rings" is not). In contrast, a sentence subject that includes an "and" as part of the subject (e.g., "Rising productivity and long-range profit . . .") is typically a plural subject, and therefore a verb that goes with a plural subject (e.g., "are," "reveal") must be chosen.
A simple way to check whether your subjects and verbs are compatible is to supply a mental "they" for a plural subject and a mental "it" for a singular subject. (Grammatically, the phrase "The speed of the downdrafts was intense" is the same as "It was intense"; the phrase "Two of the variables are incorrect" is the same as "They are incorrect"). The longer or more complex your sentences are, the more likely you are to have to apply a mental test to your subject/verb agreement at times.
Especially if you find that you are having consistent subject/verb agreement problems, you must make it a habit to do the following:
- Identify the subjects and verbs of your sentences, putting aside the other elements of the sentence momentarily.
- Test the subjects and verbs for compatibility, if necessary by mentally supplying "they" for plural subjects and "it" for singular subjects.
- Remember that a sentence subject that includes an "and" is typically a plural and will therefore need a verb that agrees with a plural.
- If the meaning or grammar of the sentence is unclear, revise so that the subject and verb are closer together in the sentence. Thus, the sentence grammar will be simplified both for you and your reader.
To further test and polish your grammatical skills, try out the quizzes at the following sites:
Quiz on subject/verb agreement from Capital Community College
Fill-in-the-blank subject/verb agreement quiz from the City University of Hong Kong