grammar - Can adjectives always be used as nouns when they denote a plural and are preceded by the definite article?

An adjective appears to be used as a noun when denoting an animate plural and preceded by the definite article:

'The successful are those who strive.'

'The foolish are those who procrastinate.'

Is this always the case?

Answer

Yep. Because there is always an assumed "people" attached. So long as it's an adjective that can reasonably be used to describe people, you should never run into an issue.

If you ever feel uncomfortable with your construction, just substitute "X people" for your "the X" and see if your sentence still works grammatically.