Certainty and uncertainty ‘Certainty’ is the firm belief that something is true. ‘Do you think it will rain today?’ ‘I am certain it is going to rain.’ You can express certainty by saying: ‘I am confident it will rain.’ ‘I am positive it will rain.’ ‘I am sure it will rain.’ ‘It will definitely rain today.’ Uncertainty is the state of being unsure. You don’t know if something is true, or you haven’t decided. ‘Do you plan to go to university when you finish school?’ ‘I’m still uncertain about that.’ You can express uncertainty by saying: ‘I am not sure.’ ‘I may go.’ ‘I haven’t made up my mind.’ ‘I might go.’ ‘I haven’t decided yet.’ Flickr CC: Viewminder