Noumenon is something opposite to the phenomenon. Something that does not exist in our "phenomenal world". For example, some idea may be a noumenon, as I understand it.
I dare to assume that you took it from the English "no-man" (man-no, that is, refusing everything and insisting on his own). In general, use it as you please, just remember that other people may be completely unaware of it, and this can create some difficulties. Good luck!
I do not know at all what a noumenon is, but it is already in this sentence!
Who knows what a noumenon is, he can easily voice his ideas and we will also comprehend. :)
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Guys, these are example sentences, as the author of the question asked .. !! Why minus.?
For those who do not know the term ... "Noumenon" is an idea or event that can be comprehended. "Phenomenon" is an unexpected phenomenon, but "Noumenon" is quite common and understandable.