Common mistake number (of) years

Common Grammar Mistake: Incorrect use of the preposition "of" with "number (of) years"

One of the most common grammar mistakes that people make is the incorrect use of the preposition "of" with the phrase "number (of) years." Many people mistakenly include the preposition "of" after the word "number" when referring to a specific duration of time. However, this usage is actually grammatically incorrect.

The Correct Usage

The correct way to express a specific duration of time using the phrase "number of years" is to omit the preposition "of" and use the phrase "number years" instead. For example:

  • Incorrect: She has been living in the city for a number of years.
  • Correct: She has been living in the city for a number years.

As seen in the correct example, the phrase "a number years" is used without the preposition "of."


The reason for this common mistake is often the confusion between the phrases "a number of" and "a number." While both phrases refer to a quantity or amount, they are used in different contexts. The phrase "a number of" is used when referring to an unspecified or large quantity, while the phrase "a number" is used when referring to a specific quantity or count.

When expressing a specific duration of time, such as "number years," there is no need to include the preposition "of" because the phrase "number" already implies a specific count or quantity.

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number (of) years mistake examples

  • Incorrect:
    For a number years, I was a caretaker.

    For a number of years, I was a caretaker.

  • Correct:
    Each egg and skin has been assigned a number by specialists.
  • Correct:
    Loop until a number variable reaches 4.
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