ABSTRACT
This chapter discusses five "facts" that should justify the logician's interest in signs in general. The first "fact" of the 1909 "Preface" is what Murphey had called the "reduction of illation to sign relation". The second "fact" is that reasoning can be understood without explicit reference to psychological processes, and recognition of this second prevents any psychologistic consideration from entering into logic. The third "fact" is that, since an argument is a sign, its component elements, and the components of those components, must be signs as well. The fourth "fact" is that logical and non-logical signs share common properties, and thus a broadening of the notion of "sign" and consequently of logic's horizon is needed in order to more finely investigate and fully understand both the similarities and the differences between all sorts of signs. The final "fact" simply assigns to the social group of logicians the task of engaging in the scientific activity of analyzing and classifying signs.
