 In addition, it should be noticed that it is a crucial feature of the Pericean system that the expressions \(F(x){\sim}q\) and \({\sim}F(x)q\) are non-equivalent. This certainly gives rise to a serious challenge when confronted with everyday intuition. In fact, it is rather difficult to make a clear distinction between the two expressions in terms of natural language. E.g. it is doubtable whether a distinction between “tomorrow it will not be sunny in London” and “it is not the case that tomorrow will be sunny in London” will be accepted as sufficiently clear.