We do a good job using the correct singular and plural forms of most nouns, because the process isn’t tricky; you just add an “s” or an “es” or an “ies” to make the plural form. But a few words that come to us from Latin and Greek don’t follow the normal pattern. As a result, their singular and plural forms are often confused or unknown.

Here’s Why: It hardly seems fair that a dead language causes trouble for us in English. “Media” is plural, of Latin origin, referring to a group of vehicles through which ideas are communicated. The singular form is “medium.” So in the example sentence, when we use the plural form “media,” we need to follow it up with the plural verb “are” instead of the singular one, “is.” There is one case in which many usage experts are comfortable treating “media” as singular, and that is when the group of vehicles is being referred to as a collective, as in The media has become an institution just like the government. However, you can avoid having to figure out whether a singular sense is acceptable or not simply by treating “media” as plural in every case—then you’ll always be correct. Conversely, when you’re referring to just one of the vehicles through which communication happens, remember to use the singular form, “medium.” Here are some correct examples of each:

There has been a trend lately toward making a plural out of the word “medium” by simply adding an “s” to get “mediums.” One sees this in print from a range of sources, some downright respectable. For example, you might read, He used several mediums to reach his audience. However, this is a recent trend, and most well-spoken folks have been carefully educated that “media” is the plural of “medium.” So you would be better off sticking to that traditional distinction if you want to be sure that your listeners or readers know you know what’s right.

Here’s Why: “Data” and “datum” work just like “media” and “medium.” The “a” ending is plural; the “um” ending is singular. The only difference between the two examples may be this: The use of “data” as a singular goes down a little easier with usage experts than the use of “media” as a singular. And that’s because facts often seem to travel in packs—so scientists and researchers typically think of data as a collective term. The bottom line is this: You’ll always be correct if you treat data as a plural. But when your meaning is focused more on the string of facts taken together as a group, using “data” with a singular verb won’t get you thrown in jail. It’s a judgment call. Here are additional correct examples of the plural sense of “data”:

Here’s Why: Another term from Latin: This one has several forms you should know. One male graduate is an “alumnus.” Two or more male graduates are “alumni,” pronounced with a long “i,” and never, ever, with an “s” at the end, as in the incorrect example. Two or more graduates of different sexes are also called “alumni,” as in our corrected example. One female graduate is called an “alumna,” and two female graduates are referred to as “alumnae,” spelled with an “ae” at the end, but rhyming with “knee.” An example of each are:

Here’s Why: “Criteria” is the plural of “criterion,” a word of Greek origin that means “standard” or “measure.” In this sentence, the woman has only one measure by which she judges men acceptable or not, so we should use the singular “criterion,” and wish her the best of luck. Separately, remember to use a plural verb whenever “criteria” is your subject. For example, it’s the criteria are and not the criteria is. Additional correct examples are:

Here’s Why: “Phenomenon,” which also comes to us from Greek, means an event that is observed through the senses rather than by thought. The plural form is “phenomena” not “phenomenons.”

Here’s Why: Okay, so you probably don’t use the full word every day; you just say “memo” or “memos” instead. And that’s fine. But when you do use the full word, remember that the plural form of “memorandum” is not “memorandums,” it’s “memoranda.”