A verb needs a subject in order to carry tense. For example, I is the subject of would have made:Originally Posted by jack
I would have made him turn around.
The verb 'turn around' remains in its base form because it doesn't have a subject. The pronoun 'him' is the semantic subject or do-er of 'turn around', but it's not the grammatical subject of 'turn around'. It's the grammatical object of 'made'. 'him' can't be both the object and the subject of two different verbs.
In short, since 'turn around' lacks a grammatical subject, it remains in its base form: turn around.
I would have made him turned around. (Not OK; 'turned' doesn't have a grammatical subject).[/u]