If you want to avoid undermining your credibility, there's two things to watch for in your writing: subjects and verbs.

What at first seems like a simple rule of grammar — singular subjects takes singular verbs and plural subjects takes plural verbs — quickly becomes complicated by special cases.

Here's a few of those exceptions:

1. Nouns ending in s

Some nouns ending in s such as news, lens and summons take singular verbs.

"The news from abroad is (not are) disturbing."

2. Nouns ending in ics

Many nouns ending in ics are singular or plural depending on how they're used. According to William Sabin's "The Gregg Reference Manual," "When they refer to a body of knowledge or a course of study, they are singular. When they refer to qualities or activities, they are plural."

"Because ethics define an organization's integrity, ethics is commonly taught in M.B.A. programs."

3. Collective nouns

Collective nouns are words such as company, board and staff that are singular in form but refer to plural groups. They may be singular or plural depending on whether they're referring to the group as a unit or to the members of the group acting separately.

"Our staff is conscientious" and "The staff do not agree on whether they should vote to strike." (If the plural collective noun sounds awkward, insert members or the members of, as in "The staff members do not agree …")

4. The number and a number

The number takes a singular verb; a number take a plural verb.

"The number of students graduating from college with crippling debt is worrisome" and "A number of factors are responsible for this increase."

5. Fractions

Fractional expressions are singular or plural depending on whether a singular noun or plural noun follows or is implied.

"More than two-thirds of the public thinks racist cops should be fired" and "More than one-half of our officers agree."

6. Subjects and complements

Subjects with a linking verb (a form of to be) are either singular or plural according to their number even if the predicate complement (the thing they refer to) differs in number.

"One problem with raising the minimum wage is fewer jobs" and "Higher wages are the key to a growing middle class."

Because of differing notions regarding the rules of formal grammar and common usage, not all grammar books agree on every point of my advice. My recommendations are based on Gregg's, as it is commonly called, an excellent guide for on-the-job writers.

Oops. Almost forgot to mention the errors in the first three paragraphs of this column. As I'm sure you noticed, my first four verbs should have been plural rather than singular.

Also, as you may have noticed, using there's rather than there're with plural complements is becoming increasingly common, even among educated writers and speakers.

Remember: There's only one of you, and there're two elements in the subject-verb relationship — and those two elements must agree in number: singular-singular or plural-plural.

Mostly, anyway.

Stephen Wilbers offers training seminars in effective business writing. E-mail him at wilbe004@umn.edu. His website is www.wilbers.com.