Subscribe to The Chicago Manual of Style Online
Usage and Grammar
Q. Is it acceptable for the subject of a sentence to use “(s)” to indicate a possibility of plurality? If so, should the verb that follows be singular or plural? The attached form(s) indicates the required accounts or The attached form(s) indicate the required accounts?
A. The “(s)” construction works only when the noun in question is not the subject of a sentence. Instead, you can use the plural alone, which we usually understand to include the possibility of a singular meaning: The attached forms indicate the required accounts. Or, if you don’t think that’s clear enough, be more explicit: One or more attached forms indicate the required accounts. Or you can rewrite to cast the “(s)” word as something other than the subject of the sentence: Required accounts are indicated by the attached form(s).