Here we examine the gradual acknowledgement of the distinction between contradiction and contrariety in the development of the so called Middle Wittgenstein's philosophy of logic. Four decisive episodes are then investigated: The first is to be found in the tractarian passage 6.3751, in 1918, where Wittgenstein identifies the color exclusion with the contradiction; the second episode takes place in 1929, when he acknowledges that some exclusions do not have the form of a contradiction; the third moment happens in December 1930, when Wittgenstein maintains that we should introduce additional rules to make the exclusion by contrariety have the form of a contradiction; and at last, in January 1931, Wittgenstein defends that these additional rules are postulations. This moment hallmarks inter alia the consolidation of his image of logical systems as games.