This is post is going to be at the wholesale, rather than retail, level. It applies to investing, and to anything else that requires understanding.
I would describe my philosophical stance these days, for the past decade or more, as Jamesian Platonism.
This is a school of thought that, to my knowledge, contains only one adherent. He happens to be the guy who blogs here.
So, what do I mean by the name, Jamesian Platonism?
From Plato, I take the idea that what we see and experience is perception, which only dimly, and only in part, reflects reality. Reality itself is always beyond our reach. And probably, reality is abstract and more like math than like daily life. If it makes any sense to speak of "ideas in the mind of God," I imagine them to be more like equations than prose. That is a way of thinking about something that is really beyond what our brains are capable of handling, so, do not take me too literally.
From William James, I get the idea that there is no reason to commit to any one school of thought. Somewhere, but I don't recall (or much care) where, James or one of his adherents says that philosophy is best thought of as a hall with classrooms on either side. We should not spend all of our time in one classroom. Use idealism when it helps; materialism when it works better. The whole idea of pragmatism is the willingness to use each philosophy insofar as it is useful, but not farther. Poke your head in and out of the various classroom, if, when, and as they are relevant.
OK, those are the ingredients. But, again, what do I mean by Jamesian Platonism?
I think in some deep sense that Plato is right, that we can't see things as they really are. But because of that, we need all the tools we can to get a grip. So I take a Jamesian approach to trying to get the best grip on reality that I can.
My friend Josh May (gated Financial Times link) tells me that I need to give an illustration or two. Josh is rarely wrong.
So: an example in daily life would be that if you are navigating, there is no need to attached to any particular map. A map of Nashville is useful only if you are in Nashville, not Miami. And, for that matter, each map of Nashville will have certain flaws, and has to leave things out. Some show you where roads are; some show population density; some show tourist attractions, etc. Nothing can show it all, because the only truly accurate 3-D map of the city is the city itself, and that is too big to carry around in your pocket.
In investing, an example is the different ways of valuing the stock market as a whole. To pick just a few interesting ones, there is the Shiller 10-year P/E, the ratio of market value to GNP, and the ratio of market value to replacement value (Tobin's q). You can look at each of these assuming that alternative investments in the bond market are rationally priced, or you can assume that bonds may be mis-priced as well. The key is having some sense of the insights and limitations that characterize each method.