noun, の adjective
A temporary theory isn't one that's set in stone yet. In fact, it's not really a theory at all, it's more of a hypothesis.
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.
I came up with the hypothesis that this soil is very good for citrus fruits like clementines and lemons.
We need Koichi's help to prove that this hypothesis is correct.
I think that’s interesting, but if you want to write an article about that topic you need to find data to prove your hypothesis.