I should think so/not

I should think ˈso/ˈnot

(also I should think she, etc. ˈis/ˈdoes/ˈdid, etc.) used for emphasis when agreeing that something is right or correct: ‘He didn’t give the waiter a tip.’ ‘I should think not, after such bad service.’‘He finally apologized for what he said.’ ‘I should think so.’‘I’m very angry with my son.’ ‘I should think you are. He’s behaved very badly indeed.’
See also: not, should, think