How should I judge if the adjective needs a hyphen?

Such as "highly ranked" or "red-haired"?

Thank you for your attention:)
chivalryHow should I judge if the adjective needs a hyphen? Such as "highly ranked" or "red-haired"?Thank you for your attention:)
When two adjectives work together to modify a noun, they need to be joined with a hyphen.

1) She is a highly-ranked official. She may be a ranked official but she is not a 'highly official', so you need the hyphen.

2) He is a cute red-haired little boy.

He is a cute boy and a little boy too, so those two adjectives each work alone to describe the boy. (no hyphens)

But he is not a red boy; he is a 'red-haired boy'. Those two words work together to describe the boy, so they have to be joined with a hyphen.

on the other hand...

"highly ranked" can be an adverb modifying a adjective.

A. Is she a ranked tennis player?

B. Yes, in fact she is highly ranked. (Note that this sentence has no 'a' and no noun. There is a linking verb, an adverb and an adjective.)

'red-haired' or 'red haired' not followed by a noun is more difficult to comment on, and I didn't find any good references.

but....

a) People are not referred to simply as 'haired'.

b) Although sometimes adjectives can function as adverbs, we don't clearly have an adverb-modifying-adjective situation here.

c) Therefore, I would say 'She is red-haired.' But lacking special context, it is more common to say 'She has red hair.'
chivalryHow should I judge if the adjective needs a hyphen?
Follow the guidelines given in one particular style manual that you like. Authorities disagree on occasion. I don't use a hyphen for an adverb-adjective combination, especially if the adverb ends in -ly. highly ranked. I believe others do. I do use a hyphen for any of those combinations with a body part and -ed. short-legged, red-haired, long-armed.

Most hyphenated compounds drop the hyphen in predicate position.

This is a well-known formula, but This formula is well known.

CJ