Interrogative adjectives are adjectives typically used to make questions. Like other adjectives, interrogative adjectives typically precede the noun they modify. The three interrogative adjectives are what, which, and whose, all of which can also function as interrogative pronouns. As such, it is important to understand and identify their function in a sentence so as not to confuse interrogative adjectives with interrogative pronouns. When used as adjectives, what, which, and whose will typically precede a noun, while their pronoun counterparts would rather be standing alone and could not be modifying anything. You may also see interrogative adjectives referred to as interrogative determiners, as their use is somewhat similar to that of the determiners a, an, and the.

Whose

Each of the interrogative adjectives has a unique purpose. Whose is used to indicate possession of the noun it modifies.

Whose notebook is this?

Here whose modifies the subject notebook to ask who the owner of the notebook in question is.

Does anybody know whose car is parked over there?

This time whose does not begin a direct question, but it is still used to inquire about the ownership of the car.

I don’t know whose idea this was.

Despite their name, interrogative adjectives do not always make questions. In this example, whose is simply used to indicate the owner of idea, although the owner may still be unknown or unspecified.

What

What is usually used to show a choice made from an unknown or unlimited number of options, although it is sometimes used interchangeably with which to indicate a choice from a limited number of options as well.

What song would you like played for your entrance?

The use of what indicates an unknown or unlimited choice of songs. Since the number of songs in existence is so vast and unknowable, what is the appropriate interrogative adjective to show that the options are nearly endless.

I don’t know what color scheme to use for the invitations.

The number of perceivable colors may technically be limited, but the possible combinations for color schemes is nearly limitless as far as most of us are concerned.

I wonder what kind of cake will be at the party.

The possible types and flavors of cake presents another unknown or seemingly limitless number of options to choose from, making what the appropriate interrogative adjective.

We weren’t sure what size to order the shirt in.

Here is an example of what being used in a place where we also could have used which. The number of normal clothing sizes is clearly not unlimited, especially when considering that only a few sizes might make a good fit for a specific person, but what and which are often used interchangeably.

Which

Which is generally used to indicate a choice out of a specific or limited number of options.

Which song would you like played for your entrance?

When we ask a question with which rather than what, it is implied that the options are somehow limited. When faced with a question beginning with which, we would usually infer that we have a limited number of options. For this example, we could add more context by saying something like, “Which song from this list would you like played for your entrance?”

I can’t wait to see which team wins the tournament.

There must be a set number of participants in a tournament. Therefore, the number of possible victors is limited, making which the best interrogative adjective for this example.

Alexei went through all of his old clothes, but he still couldn’t decide which shirts to get rid of.

The number of shirts in one’s possession is clearly limited and knowable, so which is the appropriate interrogative adjective here.