Time for a list of new questions! A great many questions!
石、岩、岩石 How are these words different? Is 岩 a different size? Does it sound more like a boulder (I notice there is the mountain radical in the kanji)? Is 岩石 more scientific/literary/technical? It's kango, which is why I was thinking so.
What about
:
1. 谷 vs. 渓谷 Is just one more literary/scholarly/scientific?
2. 増す vs. 増える synonyms? They're both native Japanese intransitive verbs meaning "to increase."
3. 分量 and 量
4. 減少する and 減る—is the former just more technical/formal/stiff sounding?
5. 省みる and 反省する—same as in #4?
6. 空の and 空っぽの for "empty"—how are they different? The latter sounds "cute" or very conversational to my ear.
7. 固い／堅い／硬い—This can be passed upon. I know it's a bit tougher, and reading the Japanese explanations made it difficult. I think the first is a bit more like "unchanging" like being stubborn or something.
8. バス停／停留所—Is the latter just more like what you'd see in a journal article or something more technical?