Ilúvatar's other theme.

[Nilpaurion Felagund]

It is said that:

[T]he Children of Ilúvatar were conceived by him alone; and they came with the third theme, and were not in the theme which Ilúvatar propounded at the beginning, and none of the Ainur had part in their making.

The Ainulindalë--emphasis mine

Now let us look at some paragraphs of the Ainulindalë:

. . . Ilúvatar say and hearkened until it seemed that about his throne there was a raging storm, as of dark waters that made war upon one another in an endless wrath that would not be assuaged.
Then Ilúvatar arose, and the Ainur perceived that he smiled; and he lifted up his left hand, and a new theme began amid the storm, like and yet unlike to the former theme, and it gathered power and had new beauty. But the discord of Melkor rose in uproar and contended with it, and again there was a war of sound more violent than before . . .
. . . Then again Ilúvatar arose, and the Ainur perceived that his countenance was stern; and he lifted up his right hand, and behold! a third theme grew amid the confusion, and it was unlike the others.

ibid--emphases mine

So, the third theme birthed the Eruhíni. But Ilúvatar intervened twice during the course of the Music. My question is: What was that other theme for?

I used to think that the other theme was where Eru made the Quendi (qv.). Yet the third theme was clearly labelled, and it was the one credited for the creation of the Children of Ilúvatar. So I have doubts now with this theory.

The other is that there were a few of the Ainur who had been quiet, and Ilúvatar purposed for them to begin their theme only after he has given a signal--the uplifted left hand:

[Ilúvatar] spoke to [the Ainur], propounding to them themes of music; and they sang before him, and he was glad. But for a while they sang only each alone, or but few together, while the rest hearkened; for each comprehended only that part of the mind of Ilúvatar from which he came . . .

ibid--emphasis mine

What do you think? Am I correct in my assumptions? Or should I stick to planting rice?