I don't think Tolkien was worried too much about the idea of good oaths and bad
oaths, but I will be the first to say I never met the man and am not totally
sure on this. It strikes me that the 'bad oaths', especially the oath of
Feanor, are oaths taken out of pride, or hubris if you prefer the Greek term
(sorry I've been taking a lot of Greek Lit classes recently). The mindset
behind the oath is the biggest thing. I don't think the message is about
not taking oaths, but about not being overly proud. Feanor got into
trouble because he went against the Valar and against his own people, something
he seemed quite willing to do even without his oath. Those who take oaths
with little thought of themselves and without hubris are better people, not
because of the 'good oath' but because of the good character. I think the
oath is less significant than the pride or lack of behind
it.
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for you beautiful ones my thought
is not changeable
--Sappho