This is a TOEFL question:

The orbit of a celestial body is usually in the shape of ellipse.

The solution says that the word "ellipse" is ungrammatical, but I don't know why. I think that word is not wrong, and doesn't need to be corrected. Can anyone explain this to me?

  • 5
    You can also say "The orbit ... is usually elliptical". Aug 6, 2015 at 12:19
  • @TRomano Much more elegant
    – Cruncher
    Aug 6, 2015 at 17:38
  • That's not a question, it's a statement. Are you supposed to say whether it's right or wrong, say why it's wrong, correct it ...? And a single word, so long as it actually exists, can't be ungrammatical. I think you need to add some more info here, and actually post what the book says without paraphrasing.
    – user22062
    Aug 7, 2015 at 9:17

2 Answers 2


The word ellipse on itself is not an ungrammatical word, but it is missing an article. Correct would be:

The orbit of a celestial body is usually in the shape of an ellipse.

Ellipse is a noun in the singular form here, and because it is a countable noun it needs an article. The indefinite article a(n) is needed here.


English is a strange beast. Some grammatically correct examples: In the shape of an ellipse. In the shape of a circle. In the shape of an octagon. In the shape of a square.

When the noun starts with a vowel, an is used instead of a, the only exception to this is when a noun has a consonant that isn't pronounced and has a vowel after it, such as 'hour'.

  • 2
    Just like to point out that the a/an applies to the word directly after it which may not always be the noun. E.g. it may be "an ellipse" but when we add an adjective it is "a beautiful ellipse".
    – Hannesh
    Aug 6, 2015 at 23:55
  • 2
    For "a/an", I usually simplify the rule to "if the next word starts with a vowel sound". This covers anomalies like "a uniform" and "a user" Aug 7, 2015 at 8:39

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