In our day, almost all professional philosophers who explicitly relate their thinking to some known logical theory have opted for modern logic, a science developed since the second half of the last century, in spite of all the questions which it leaves unsettled. Many logical views which were once commonplace have turned out to be untenable, and are now as a rule avoided. The so-called traditional logic, flourishing among philosophers of the nineteenth century, has practically disappeared from the scene of theoretical philosophy.