Confusion over SURU verbs (する）

Good afternoon everyone.

Can someone please give me some guidance here as I'm pretty lost.

I speak Japanese to a basic level but have been studying kanji for a few months now, and through kanji has bought new vocab. With the new suru verbs i have learned it feels like some of them are just copies of what the plan verb has to offer and I'm never sure when or if its appropriate to use the suru verbs. Please see my specific question below;

１

住む to live
SOMEONE と（一緒に）住んでいます。
SOMEONE と （一緒に）同居しています。

２

信じる to believe or 信用する

3

進める to continue or 進行する


I hope my questions make sense and a Japanese speaker can answer.

Thank you,

David

In both #1 and #2, the verbs are virtually interchangeable. You can use 一緒に住む, or you can use 同居する, and both will be equally understood. In your example #3, I think there is a problem in that the two verbs are not identical. 進める means to proceed with something (some paperwork or some procedure), while 進行する means to advance or to make forward progress. Similar, but not interchangeable.
In any event, to answer your question, there will be no shortcut for memorizing which -suru verbs are interchangeable with their stem form. It is a case of exposure, repetition, memorization, experimentation, etc...

Majestic said:

In both #1 and #2, the verbs are virtually interchangeable. You can use 一緒に住む, or you can use 同居する, and both will be equally understood. In your example #3, I think there is a problem in that the two verbs are not identical. 進める means to proceed with something (some paperwork or some procedure), while 進行する means to advance or to make forward progress. Similar, but not interchangeable.
In any event, to answer your question, there will be no shortcut for memorizing which -suru verbs are interchangeable with their stem form. It is a case of exposure, repetition, memorization, experimentation, etc...

Click to expand...

Thank you!

1)
と is the key. People と（一緒に）住む is the same as と同居する, as already answered, but 同居する can't be used for "to live alone" of course. Besides, 一緒に同居する is repetitious, or rather it could be misinterpreted that they both live with other person(s) each other, not they live together.

2)
信じる is more broadly used. For instance, 仏教を信じる and 仏教を信用する are different in meaning, something like "to believe in" vs. "to trust".

3)
Other than what Majestic-san explained, you need to pay attention that 進める is transitive but 進行する can be both transitive and intransitive.

○会議を進める
×会議が進める
○会議が進む

○会議を進行する
○会議が進行する

In conclusion, your impression "it feels like some of them are just copies" is not correct. You need to memorize each cases, as already pointed out.