Know
From Creolista!
Irregular Verb
know /no/, knew /nu:/, known /non/
Syntax
Thinking is an activity, but you either know something or you don't. (cf. state verbs vs. activity verbs) As a result, the verb is incompatible with be Ving. The present participle knowing, of course, still exists (it's even an adjective), but it is not used with be.