He keeps himself in good health.
(What is the part of speech of 'in good health'? An adjective phrase or an adverbial phrase? I think we can substitude 'healthy' for 'in good health'? Then, is 'in good health' an adjective phrase?)
1 answer
Yes, that phrase is an adjective phrase. If it were adverbial, it would be describing "keeps" -- and that makes sense, too, but the phrase is right after "himself" so that is most logical.