Are the words contentious and controversial synonymous AND interchangeable? or is there some difference in some contexts or in emphasis? For example, take this sentence I found in an excerpt from a book, "....the answers would be complicated and hugely revealing. The answers would also be contentious and controversial." if they are indeed interchangeable then it should have been considered redundant to use both words in a sentence, so I am wondering if the two words have slightly differing meanings.
When applied to things like issues (that might generate contention/contentiousness/controversy) it's probably pointless trying to impose some kind of distinction.
But when applied to people, usually a controversial person is someone that others argue about because they have different opinions about him (not necessarily because of anything he says - perhaps some people just don't like the colour of his skin, or the fact that he had a sex-change op).
On the other hand, a contentious person usually means someone who habitually argues. In principle, such a person may generate very little controversy (everyone else may be in complete agreement that he's tiresomely quarrelsome over things no-one else really cares about).