The first premise I start with is that we do think in threes, at least when we are conscious and certainly when we will to do so.
The second premise is that if this is so the initial starting point would be the realm from which all signs emerge. To me this came up as Reality so that was and remains my notion of Firstness. (I am NOT trying to preempt Peirce, merely to acknowledge a linkage.)
I conceived of Triadic Philosophy as a conscious process and of the triad as deriving from icon (reality) to index to symbol. Rather spontaneously, I chose Ethics as the second (index) and Aesthetics as the third. Actually I have for four decades relied on an ethical index derived from my work in music and with teaching kids to sing the gospel of Mark. When this is done, at least in my declension, the values that pop up are tolerance, helpfulness, democracy and non-idolatry. If that is not an index, what is?
Then it followed (to me) that in terms of my elaboration of the pragmatic maxim the purpose of thought should be an action or expression, something that can be known and measured for impact. By making aesthetic my third in the triad, it opened up a world to me in which we move past an ineffective ethics and a terribly confined notion of aesthetics to something closer to reality.
I should mention that my laboratory is Twitter and that premises such as those discussed here are regularly honed to and submitted to a large group of folk @stephencrose who may or may not respond, but whose reactions are of inestimable value in determining the effectiveness of communications.
I should note also that I have taken with great seriousness Peirce's suggestions regarding memorial maxims. What is a tweet if not at least a stab at such?
As to what this looks like, I do contend that Reality Ethics Aesthetics is a workable triad for the conscious method of doing triadic philosophy and that it corresponds (possibly even theoretically) to Peircean notions of firstness, secondness and thirdness, first second third and 1 2 3. I do have some questions about Peirce's brief description of universes of experience in NA (The Neglected Argument).