Common Errors in English: A, An, One

Don’t say: “I took one pen and started to write.”

Say: “I took a pen and started to write.”

Use one when the number is important; when you want to emphasize that it is only one (not two or three or more):

  • One of these eggs is rotten, but the others are OK.
  • I wanted to buy three CDs, but I didn’t have enough money, so I bought only one.

In all other cases, when the fact of being “one” is not important, use a / an:

  • I had an omelet for breakfast.
  • I bought a new CD yesterday.

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