I think mourning versus melancholy is a good distinction, provided you allow for forms of depression that aren't forms of grief. (They can be, say, forms of despair instead.) Another helpful bit of Freudian thought also came to recently by way of Cavell, namely the idea of mourning as repetitive disinvestment. The "repetitive" part was particularly helpful, as it reassured me that the repetition of mourning is not the repetition of, say, obsession.

Useful post! *points up* And this is my username here on LJ.