That's a great question. Your cousin comment notes that Peirce has influenced my thought. He had something of a fascination with three because of structural pro

That's a great question. Your cousin comment notes that Peirce has influenced my thought. He had something of a fascination with three because of structural properties. In essence he saw the mathematical relation as a triad and so he considered three in some way essential to logic and what he called semiotic[1]. Some of that has probably rubbed off on me. I don't think it's a magic number, just a common one. I happen to know of three normative sciences. I would gladly learn about a 4th, 5th, or more if they exist, especially if they share the same broad intellectual utility. It can also be a case of lumping versus splitting[2]. Postulating that logic, ethics, and aesthetics together are somehow exhaustive, one could still conceivably divide any of them into further subdivisions and spawn new normative sciences that way. I don't believe that would help me make my thoughts clear to myself or others, but, pleasantly, if someone else discovers that it does help then they will have an easier time convincing me too! Conversely, I can't imagine how lumping any of the three I listed together would be an aid to understanding. [1] Not really what postmodernists mean. See https://plato.stanford.edu/entries/peirce-semiotics/ https://plato.stanford.edu/entries/peirce-semiotics/ [2] https://en.wikipedia.org/wiki/Lumpers_and_splitters https://en.wikipedia.org/wiki/Lumpers_and_splitters