Noumena is the world of Essential, Eternal Ideas -- Phenomena is the world of Appearances ...

I.

"Noumena is the world of Essential, Eternal Ideas --"

A Noumenon, such as 'essentia', IS an essential idea, may be even sort of an eternal idea.

... 'idea', thus, is taken as 'essential idea', the essential idea of 'essentia' (Wesenheit); onlo-logical center in a priori relation to 'entes', 'entium' 'entibus' (the ontic; plural) ...

voila, the onto-ontological difference with Thomas of Aquin, De ente et essentia.

Aquin, thus, has got the onto-ontological difference 'between' 'entia' (plural) and 'essentia' (one) ... 'essentia' even taken as "regulative Idee" (I. Kant).

But there would be no 'essentia' without 'entia' and there are no 'entia' without 'essentia'; this means, the title of the topic better were "De entibus et essentia" ... monas monadum ... essentia entium ...

II.

Phenomena is the world of Appearances

Phenomena: 'sharply taken' as "world of appearance" AND 'ad-perceptio' of the world of appearance, i.e. "Apperzeption" in space and time (Kant), in space-time (A.Einstein, I.Prigogine) ... appearance AND apperception then; not to forget Stephen Hawking and the BigBang.

Very interesting what you give 'during' the run of your discussion.

Regards - jh