Q) "What type/kind of (a) compressor is used in a rocket engine?"

A) "The compressor used in a rocket engine is called the rocket-engine compressor and it is not that type/kind of (a) compressor that is commonly used in other fields of engineering........"

All that I'm confused of is whether or not to use an indefinite article before "compressor" in the above two structures.

And would it be grammatical, if I pluralized the above interrogative structure as below?

Q) "What types/kinds of compressors are used in rocket engines?"

  • The short answer is skip the article. If you want to know more, I recommend our sister site, English Language Learners.
    – Dan Bron
    Commented Sep 26, 2015 at 11:59
  • To me, "kind of a <N>" is colloquial, and also typically American (I'm UK). It's not something I would say, but I hear it often enough.
    – Colin Fine
    Commented Sep 26, 2015 at 12:03
  • 1
    ""What kind of compressor" (both singular) assumes or implies a singular answer is expected. "What kinds of compressor" implies that there is one compressor per rocket, but it may be of various kinds. What kind of compressors" implies that multiple compressors, of various kinds, might be used in the same rocket. "What kinds of compressors" implies that multiple compressors of multiple kinds are used, though not necessarily at the same time in the same rocket. However, the hearer might respond in the singular or the plural to any of these queries. Commented Sep 28, 2015 at 12:52
  • Oops, I meant "What kind of compressors" implies muliple compressors per rocket, but all of the same kind. Commented Sep 28, 2015 at 13:01
  • And no, you do not need nor should you use indefinite article. Commented Sep 28, 2015 at 13:01

1 Answer 1


There is a strong tendency that indefinite articles are not used even if they are mandatory, so we can see "what kind of person / fool" without "a" quite often. I think it should be regarded as a trend instead of any grammatical rule change.

I would suggest using plural nouns after "of", i.e., what kind of compressors are used in a rocket engine? There is a possibility that more than one compressor might be used in a rocket engine.

Regarding your Q No. 3, it is perfectly grammatical if you are inquiring about name of plural compressors knowing that there are different type.

A type of A compressor, B type of B compressor, C...

But, there seems to be no difference between "what kinds of compressors" and "what kind of compressors" as there is not a big chance that answers could be different depending on which of the two questions being asked.

  • is it acceptable to omit the indefinite article in written forms? Commented Sep 26, 2015 at 14:36

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