used for referring back to a possibility, fact, or situation that has just been mentioned I think/suppose/expect/hope etc so:
You’re in love with Rita, aren’t you? I thought so.
so they say/so they tell me/so I understand:
I’m a quick learner. Or so they tell me.
more so/less so/very much so:
‘Is Sybil the outdoor type?’ ‘Oh yes, very much so.’