English “What” “Which” and “What kind of”

This unit covers the interrogatives “what,” “which,” and “what kind of” and when to use each one.

What vs. Which
The question words “what” and “which” are similar to one another; however, there are certain times when one is used or preferred over the other. In cases with many choices or options, “what” is the correct one. When there are fewer options, “which” is preferred.

Examples:
What are you having for dinner?
Which bike is yours?

In the first example, there are many possibilities concerning foods to eat. In the second, however, there is an implied, limited group of bikes being referred to at a particular location. Sometimes, these words are nearly interchangeable:

What flight are you on?
Which flight are you on?

A native speaker would not notice any difference in the above two examples – they are both equally correct.

Which Kind vs. What Kind
Looking at “which kind” and “what kind,” they at first appear interchangeable:

What kind of dog do you have?
Which kind of dog do you have?

The second question would be used less frequently, but both “which kind” (could imply a select subset) and “what kind” (general) are acceptable grammatically speaking.

BUT

The following question is rhetorical, which makes is awkward to use anything other than “what kind”:

What kind of person would do that?