I have read that virus is both a countable and non-countable noun. I am therefore unsure which of the following is grammatically correct.

There are six types of computer virus available. There are six types of computer viruses available.

My initial thought was to go with the first. The second simply doesn't seem right to me. Also to clarify, I'm referring to a computer virus.

  • This doesn't seem to be specific to viruses. I think any countable noun can be used in this way, eg. "There are six types of brick available". I don't think this makes "virus" (or "brick") uncountable; it is just part of the (countable) noun phrase "types of virus". – user323578 Apr 3 at 11:38
  • Part of the problem here is that no one can agree as to the plural of "virus". – Hot Licks Apr 3 at 12:23
  • All the answers and comments so far discuss when you can use the singular of a countable noun. None give examples of an uncountable use of this word. Can you please give a source for the claim that it can be used uncountably? And ideally an example sentence? – David Robinson Apr 3 at 15:52
  • @HotLicks, I think a lot of people imagine there must be some Latin-based plural but I for one don't know what it is as there are at least three possibilities. I have only ever heard viruses. Have you got any source for this disagreement about the plural? – David Robinson Apr 3 at 17:21
  • @DavidRobinson - Back when the computer virus first became a "thing" there was considerable debate. Many folks wanted to use "virii", a term with some history in the medical/biological arena. But apparently even among that audience there was little agreement. Computer nerds thus, in not untypical fashion, declared that "viruses" was the correct plural, at least in computerdom. – Hot Licks Apr 3 at 17:25

Both are fine, just as ‘There are six types of person’ and ‘There are six types of people’ are both fine. However, ‘There are six types of computer virus’ seems more natural to me. (But not sure which is better.)

And yes, ‘virus’ can be a count noun.


Whether one chooses a singular or plural after types of can depend on whether one thinks of the noun as a generic or as an aggregate of individual things.

In fact, the uniform color of several types of oranges is due to injection of an artificial dye, Citrus Red Number 2 into their skins. — John Davidson, M. Usman, Health Benefits of Oranges For Cooking and Health, 2013.

An interesting relationship exists between different types of orange and the tristeza virus. Both sweet and sour orange are highly resistant to injury when on their own roots, so that each species appears to have a high degree of tolerance of the concentration of virus it produces in its own tissues. — K. M. Smith, Plant Viruses, 2012, 32.

The plural oranges is how one encounters the mass of oranges in processing and sales. The singular orange is the orange tree, of which there are two types listed.

The same is the case with coffee beans:

All coffee beans have qualities that are remedied or enhanced by mixing them with other types of beans, and to achieve a good blend, up to eight types are sometimes used. — Valéria Vieira Sisti, Leith's Latin-American Cooking, 1998, 263.

Simply speaking there are two types of bean: Arabica and Robusta. — Seb Emina, Malcolm Eggs, The Breakfast Bible, 2013.

The plural is more the consumer product and the singular is the bean produced by a particular kind of plant.

This distinction is not especially rigid and in most cases makes little difference, just as one can say that the potato is a starchy vegatable or potatoes are high in starch. In your particular example the difference is minimal.

The standard English plural of virus, by the way, is viruses. The pseudo-Latin plural viri is limited to computer jargon. For instance, the plural of rhinovirus never has been and never will be *rhinoviri. The Latin word had no plural, but viri does happen to be the nominative plural of vir, ‘man’ (think “virile”).


According to Oxford English Dictionary, Merriam-Webster's Dictionary, Cambridge Dictionary, etc. Virus has a special plural 'viruses'.

As about the phrase 'types of...' both variants are possible, but the phrase with the plural form (... viruses) is much more frequent: https://books.google.com/ngrams/graph?content=Types+of+virus%2C+types+of+viruses&year_start=1800&year_end=2000&corpus=15&smoothing=3&share=&direct_url=t1%3B%2CTypes%20of%20virus%3B%2Cc0%3B.t1%3B%2Ctypes%20of%20viruses%3B%2Cc0

  • Note that Google Ngrams is, by default, case sensitive. So if you change your comparison to "types of virus,types of viruses" the results are very different. – user323578 Apr 3 at 11:40
  • They ARE different! – user307254 Apr 3 at 12:11
  • This is the correct Ngrams URL. As you can see, "types of virus" was much more popular until about 1985 when "types of viruses" started to overtake it and by 2000 was about twice as common. This seems to be mainly a US thing, both forms are about equal in British English. – user323578 Apr 3 at 14:01
  • Thank you. Though I can't see the difference in these two pages with different graphs. – user307254 Apr 3 at 14:21
  • I don't understand what you mean by 'special plural'. Viruses looks like a perfectly normal plural according to the rules of English grammar. Since there is no clarity about what the Latin plural would be (as it was never recorded), that makes the use of the regularly-formed English plural even more normal. – David Robinson Apr 4 at 14:20

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