suggest

TakaWhich 'suggest' do you think it is, if you use the definitions here?

To make evident indirectly; intimate or imply: a silence that suggested disapproval.

Good. Just as I thought.
Just out of curiosity, does this make sense?
Common sense suggests that better lighting (should) reduce crime.

I don't see a problem with this. I'm not sure why you put "should" in parenthesis since it's required for the sentence to make sense.
Also, "would reduce crime", "ought to reduce crime", "will reduce crime", that's all I can think of at the moment. I'm sure there are others.

TakaCommon sense suggests that better lighting reduces crime.

Should it be bare infinitive?

I've seen all the sentences used, and I believe all of them are fine.

Common sense suggests that better lighting reduces crime.

Common sense suggests that better lighting reduce crime.

Common sense suggests that better lighting should reduce crime.

Yoong LiatCommon sense suggests that better lighting reduce crime.

I can't go along with this one. It's clearly incorrect.

Isn't suggest subjective?

He suggested his girfriend go home.

New2grammarIsn't suggest subjective?

I think you mean "Doesn't suggest govern the subjunctive?", and the answer is "Yes, but only in its definition as offering advice -- not in its other meanings, such as the one being discussed here."
CJ

I wanted to say subjunctive. It's a really difficult topic and as you can see I was so confused I even misspelled the word. I wish there were no subjunctives.

Hi New2grammar

If you click on Taka's link, it will not show the contents of the link. Now you should know what I was trying to say when I mentioned it a couple of days.ago.