WHY IS THE NORMATIVITY OF LOGIC
BASED ON RULES?
According to Peirce, normative sciences are the “most purely theoretical of purely theoretical sciences” (CP 1.281, c. 1902, A Detailed Classification of the Sciences). At the same time, he takes logic to be a normative science. These two sentences form a highly interesting pair of assertions. Why is logic among the most purely theoretical sciences? What does it actually mean that logic is a normative science? In this essay I will answer these questions by addressing the question of why the normativity of logic is, as a matter of fact, based on rules.
The statement that logic is a normative science has been routinely taken to follow from the classification of the sciences that Peirce came up with in 1903, termed the “perennial classification” by Kent (1988) (cf. Pietarinen 2006a). Namely, normative logic is the “third” normative science that depends on the second or “mid-normative” science of ethics (a.k.a. practics, anthetics)—or that the second provides grounds or support for the third—and logic and ethics depend on the first normative science, which Peirce spells esthetics. Moreover, normative sciences as a