nouns

[notmyname216]

What type of noun is a noun that is normally used as a adjective?
Here are some examples:

1) The strong live longer than the weak.

"strong" and "weak" are normally adjectives but in the sentence they are used as noun. Are they abstract nouns or some other type of noun?

2) The old play house.

"old" is normally an adjective but in this sentence it is used as a noun.
Is it a abstract noun or some other type of noun?

[trustM]

I don't know the name for this BUT-when you put the definite article in front of certain adjectives, they refer to the whole class of people sharing the same feature/characteristic.
"the old"=all the people that are old=old people
"the weak"=all the weak people, etc.

[trustM]

Well, I guess this wasn't very helpful...

[Tdol]

They're adjectives being used as nouns. A noun used as an adjective would be 'shoe' in 'shoe shop', where it modifies the noun 'shop' to denote the type of shop. I don't think there are and hard and fast rules about the type of noun that can do this.

[notmyname216]

Are they called vernacular nouns?

[Casiopea]

The term you're looking for is substantive. It comes from the word "substitute".

The old citizens play house.
Form: "old" is an adjective
Function: "old" functions as an adjective

The old play house.
Form: "old" is an adjective
Function: "old" functions as a noun. It's a substantive noun, or it substitutes for (i.e., takes the place of) a noun.