I've been trying to remember this aphorism for the past week or so and I finally remembered enough of it to locate it:
"He who refuses to do arithmetic is doomed to talk nonsense." And the corollary, that in order to do arithmetic you need to be able to measure and quantify that which you are doing arithmetic on.
Not to say that there aren't things you can't quantify--sometimes you really are just doomed to talk nonsense, as witness the whole history of philosophy. :) Anyway, I'll try to remember this advice in this political silly season. There are things I like about McCain and things that scare me about Obama, but before committing the fallacy of intentions (e.g. assuming that because Obama is hostile to business and McCain is pro-growth, that McCain will be better for the economy) I will try to do some basic Back of the Envelope sanity-checking.