Mathematics doesn't deal with the real world, nor does it use induction (in the normal sense of the term--mathematicans use the word "induction" to refer to a type of recursive proof method, but inductive logic is the method of reasoning general rules from particular pieces of evidence). Triangles are an abstract concept that abide to rules that we make up, and if we make up a different set of rules, triangles no longer obey them. That's why simply measuring triangles doesn't work.<p>Economics does deal with the real world, and like any other science it's subject to the demands of empiricism rather than merely the demands of logic. You can use logical and mathematical reasoning to come to a lot of useful conclusions in physics, for instance, but we're constantly substantiating those by experiment as well, and occasionally we are wrong. (Use Newtonian mechanics to calculate the orbit of Mercury and it won't match.) Do you really think that human behavior is so much more simple than physics that we can model it without evidence at all?