I came across a diagrammed sentence in a Houghton Mifflin English (Level 10, Pub. date 1992) book where the verb act was implied to be a linking verb. To simplify, the sentence in essence said, "He acts proud." Proud was diagrammed as a predicate adjective (and, in fact, most dictionaries will say that proud is an adjective, and not also an adverb).
So, the diagram showed act as a linking verb with proud as the predicate adjective.
I balked at that, thinking that act is an action verb; however, to use proudly does not quite sound right: He acts proudly.
Assuming act is indeed a linking verb, would someone please help me understand how act might indeed be a linking verb in this case–even though when I think of act, I think of literal action, not linking.