Citation

Expressing opinion

To argue, allege, assert, assess, be convinced, believe, consider, feel, hold, judge, maintain, opine, suggest, think + that/as

To criticise

Assertion, assessment, belief, conviction, judgment, opinion, position, suggestion, view

To hold opinion

is of the opinion that

according to

as far as … is concerned

Expressing facts

Confirm, demonstrate, establish, identify, indicate, make clear, note, observe, point out, prove, show.

Neutral

Conclude, emphasise, mention, say, state, stress and write.

Source: https://guinlist.wordpress.com/2015/06/15/107-the-language-of-opinions/