A vs. an | Conventions of usage | ACT English

The a vs. an rule is one you’re likely already familiar with.

However, we still thought we’d include it. This will occasionally show up as a wrong answer choice on the ACT, and we want you to make sure you’re not fooled. Review this information and be ready for the ACT traps!

Remember that the article adjectives a, an, and the identify nouns.

So here’s the rule. When deciding whether to use “a” or “an”:

Look at the following word’s first sound
If that word begins with a vowel sound, “an” should be used. Otherwise, use “a”

Example

Take a look at this example:

An exemption was made when an error was found in the test taken by a graduate student.

Exemption and error are both nouns that begin with a vowel sound. Thus “an” is used. Because graduate does not begin with a vowel sound, “a” is the right choice.

Below, blanks have been placed where an “a” or an “an” might go. Determine what is best.

__(1)__ very hungry sparrow picked desperately at __(2)__ obvious seed, frozen at __(3)__ angle that made it difficult to harvest.

Now, you try. Go ahead and see if you can pick the correct answer for each blank:

a/an

a/an

a/an

(spoiler)

Answer:

The word “very” begins with a consonant sound, so we should be using “a” there. The other two (“obvious” and “angle”) begin with a vowel sound, and should therefore have “an” to introduce them.

Exercise

Here’s how you’ll see this concept on the ACT.

A massive, angry rhino threatened the safari group.

A. NO CHANGE
B. A massive angry rhino
C. An massive, angry rhino
D. A massive and angry rhino

(spoiler)

Answer: A. NO CHANGE

Here, the sentence is correct as is.

B and D are seeing if you know that two adjectives of equal weight should be separated by a comma. There’s nothing technically wrong with D, but it breaks the concise rule (no need to say something in five words when you can say it in four). B is identical to A except it’s trying to get you to second guess yourself and choose “a” vs. “an.” Don’t fall for it. The next word, “massive,” starts with a consonant sound instead of a vowel—therefore, we need “a” instead.

Remember, all you have to do is remember these two steps and you should do well come test day:

Key points

Know when to use “a” or “an” by doing the following:

Look at the following word’s first sound
If that word begins with a vowel sound, “an” should be used. Otherwise, use “a”