The 'certain' group
These adjectives indicate that someone is certain or uncertain of something.
certain comfortable confident convinced doubtful dubious persuaded positive satisfied sceptical sure uncertain unconvinced
I'm fairly certain he is an American.
When we both feel comfortable that Ian is established and that he doesn't need me any more I will step down.
I am absolutely positive that this is what should be done.
Many academics remain unconvinced that higher education has a problem with rising dropouts.