Simply put, Interrogative Adjectives are adjectives which modify a noun (like all adjectives do) and also ask a question.

These are the interrogative adjectives:

what
whose
which

Any sentence which begins with an interrogative adjective is a question:

Which coat is yours?
What time is it?
Whose car is blocking the drive?

Like all adjectives, interrogative adjectives modify a noun:

{adjective} + {noun phrase} + {…}

whose + dog…
what + television program…
which + famous actor in Hollywood…

Question Words

These are the so-called question words in English:

who, what, where, when, why, whose, which, how

But remember that not all question words are adjectives. Only when a word modifies a noun does it become an adjective so while we can say:

Which dog is yours?

we cannot say

* Where dog…
* Why dog…
* When dog…
* How dog…

* an asterisk at the beginning of a sentence denotes an ungrammatical sentence

Not always Interrogative Adjectives

So while what, whose, and which often work as interrogative adjectives they are not exclusively interrogative adjectives.

Which color do you prefer?
Which is your favorite color?

In the first case which modifies a noun, therefore it’s an adjective. In the second place which comes before a verb and doesn’t modify a noun in sight!

Interrogative Adjectives & TEFL

Is it worth talking about interrogative adjectives in your TEFL class?

The chances are that unless you are teaching a detailed English grammar to your class you can get through your entire career without bringing up interrogative adjectives per se. Treat them as simple question words and there’s no real need to get into the grammar of what they modify. It’s even less likely that you’ll need to get into the way in which what, whose and which can serve as interrogative adjectives one moment and pronouns the next.

Our advice would be to know what they are but only let the class know if it’s really necessary. Keep it to yourself, in other words!