How to tell the difference between predicate adjectives and action verbs

In a comment, John Lawler wrote:

A list of objects was written is a good example. It's ambiguous. It can refer either to the past event of writing the list (which is a passive, and therefore a verb), or it can mean that the list was a written list, in which case it's an adjective. Generally native speakers will choose the first -- and often not even notice the second -- because that's not a normal way to use a predicate adjective and it's easier to interpret it as a past tense passive. So you're not the only one who has trouble with this; everybody does, and one has to interpret in context.