Some foreign words are used in the English language,
and their pluralization usually follows the rules
of their language of origin. For example, Latin
singular words often end in -us (alumnus, syllabus),
and follow the Latin rule of changing the -us
to -i to create a plural (alumni, syllabi). Other
Latin words end in -um (curriculum, datum, medium),
and are made plural with -a (curricula, data,
media). Greek words often end in -on (criterion,
phenomenon), and are changed using -a (criteria,
phenomena). Because these words follow the rules
of other languages, it is best to check a dictionary
when making them plural
Note: For many foreign words, our most common
use of them is in the plural. For example, we
use the word "data" much more than we use the
word "datum," and the same with "media" and "medium."
A common error is to treat the common plural form
as a singular, in regard to subject-verb agreement
and pronoun agreement. Be sure to use the plural
forms of the verb and pronouns.
Wrong: This data is incorrect.
Right: These data are incorrect.