"Now forgotten" vs. "now-forgotten", "once powerful" vs. "once-powerful" [closed]

Ah, hyphens. I used to read a lot into these topics too, so I'll tell you what I've learned through other people and my own experience.

When an adjective phrase is formed using an adverb and an adjective there is no need for a hyphen. In your sentences, "now" and "once" are adverbs, so there is no need to hyphenate: A now forgotten era, a once powerful civilization.

If you're not one to consistently follow strict rules about grammar, think of hyphens as an aid for clarity. Only use them when it makes the sentence less confusing. This is mostly when adjective phrases use two nouns or adjectives, for example: "A chocolate-filled pastry". Even though people will understand "A chocolate filled pastry", some odd minds will read that the chocolate filled the pastry.

To sum it up, no need to hyphenate with adverb-> adjective. Your sentences are fine without hyphens.