How can you check the agreement of subjects and verbs?

A verb must agree in number (i.e., singular or plural) with its subject, regardless of intervening phrases that begin with such words as together, with, including, plus, and as well as.

• Incorrect:
  The percentage of correct responses as well as the speed of the responses increase with practice.
• Correct:
  The percentage of correct responses as well as the speed of the responses increases with practice.

Consult a dictionary (APA prefers Merriam-Webster's Collegiate Dictionary, 2005) when in doubt about the plural form of nouns of foreign origin.

For examples of agreement of subject and verb with collective nouns, see Agreement of Subject and Verb, [section 3.19 of the manual, supplemental material (PDF)].

(adapted from the sixth edition of the APA Publication Manual, © 2010)