[Lalwendë]

Some useful grist for t'mill from Osanwe-kenta:

The Valar entered into Ea and Time of free will, and they are now in Time, so long as it endures. They can perceive nothing outside Time, save by memory of their existence before it began; they can recall the Song and the Vision. They are, of course, open to Eru, but they cannot of their own will 'see' any part of His mind. They can open themselves to Eru in entreaty and He may then reveal His thought to them.

and

...a mind can only learn of the future only from another mind which has seen it.But that means only from Eru ultimately, or mediately from some mind that has seen in Eru some part of his purpose (such as the Ainur who are now in Ea).

So a Maia such as Melian might know from before Time some of the purposes of Eru, or she might have asked Eru about the future, but likewise, there are no guarantees. We are also told in the Sil that she simply loved Thingol and so took on a physical form (and in Osanwe-kenta we are told that the act of begetting children is particularly likely to 'fix' someone in physical form, so she must really have been in love!). Therefore, it could be either - I would say the 'magic' is in not really knowing the truth.


Of course, if we go down the path that Melian knew Eru's purpose, why should Sauron not have known it? And that leaves us with one of two options - evil was unavoidable as Eru made it happen, or Sauron (and the Dark Side) were actually trying to free Ea from 'fate'.

EDIT

And another thing...

Thinking about the way that the Ainur entered Ea and were then 'stuck' there until the end of Time, there is an odd occurence of one of the Ainur who does not seem to have been stuck there. Gandalf.

A great smoke rose about us, vapour and steam. Ice fell like rain. I threw down my enemy, and he fell from the high place and broke the mountain-side where he smote it in his ruin. Then darkness took me, and I strayed out of thought and time, and I wandered far on roads that I will not tell. 'Naked I was sent back--for a brief time, until my task is done. And naked I lay upon the mountain-top. The tower behind was crumbled into dust, the window gone; the ruined stair was choked with burned and broken stone. I was alone, forgotten, without escape upon the hard horn of the world. There I lay staring upward, while the stars wheeled over, and each day was as long as a life-age of the earth. Faint to my ears came the gathered rumour of all lands: the springing and the dying, the song and the weeping, and the slow everlasting groan of overburdened stone. And so at the last Gwaihir the Windlord found me again, and he took me up and bore me away. '"Ever am I fated to be your burden, friend at need," I said. '"A burden you have been," he answered, "but not so now. Light as a swan's feather in my claw you are. The Sun shines through you. Indeed I do not think you need me any more: were I to let you fall, you would float upon the wind." '"Do not let me fall!" I gasped, for I felt life in me again. "Bear me to Lothlorien!" '"That indeed is the command of the Lady Galadriel who sent me to look for you," he answered. "Thus it was that I came to Caras Galadhon and found you but lately gone. I tarried there in the ageless time of that land where days bring healing not decay. Healing I found, and I was clothed in white. Counsel I gave and counsel took.

What's this then? Gandalf seems to have gone right outside Time (as has been discussed before), but he is returned seemingly as a Fea only, judging by what Gwaihir says. The Sun shines straight through him. Does his Hroa come back to him as Gwaihir bears him along? Does it come back to him in Lothlorien? Can that be ruled out as surely even Galadriel cannot be permitted to rehouse a Fea? Note that Galadriel formed the White Council, and she is the one who clothes Gandalf in White. Is she the one who chooses the White Wizard?