If the noun after kind of is singular, do we use an indefinite article or not? For example,
- That kind of an answer is teasing.
- That kind of answer is teasing.
Which is correct?
Both are correct and grammatical. Personally I think I would usually leave out the article, but maybe not always.
I think there is a slight difference - or at least slight in terms of habits of usage. But "kind of" tends as a phrase to gravitate towards entities that actually exist and that are readily identifiable, whereas "kind of a" tends towards the hypothetical.
"That kind of car doesn't suit my purposes," says someone, speaking of a particular make and model.
"What kind of a car would it be that allowed passengers to stand?", says someone else, speaking of a car that might exist, but probably doesn't.
As I say, the difference is slight, and both forms are continually invading each other's territory, but I do think that there is a particular flavour to "kind of a" that tends towards the hypothetical.