Borhas wrote:untrue. the first two are the only assumptions required for rationality. besides which, what lay people mean when they say rational is pretttty damn similar to what economists mean when they say rational.
btw some of those assumptions are assumptions of what is preferred not what rationality is...(#3, and #4) though I guess they added them to the term "rational" so that it wasn't completely empty.
My whole point is that for economists a serial killer can be rational. If the serial killer's objective is to kill person x, has only available modes of behavior X,Y, Z, and X costs the least of the three, and if the serial killer choose mode X, killing someone, the serial killer is "rational" according to economic choice theory. Very few people would think that a serial killer can be rational.
By similar cost/benefit analysis, some economists conclude that it may be rational for individuals to eat more/exercise less than before (for arguments sake say in the 1200s) because the costs of doing so (i.e. the health costs) have gone drastically down. Again, most people think that it's irrational to not exercise, or overeat, etc.
Rationality refers to achieving your objective in the most efficient manner. Economists generally care more about the direction of the behavior rather than the magnitude (though there are obviously cases where we care about the magnitude and we might try to measure the magnitude in cases where we might not care about it so much). Say we increase the price of good x, assuming "rational behavior", we economists think that the consumption of good x will go down. How much is an empirical question - which we can try to answer, but the models will tell us the direction (that consumption will go down.. not up). Iono, I think it's a useful way of analyzing behavior .. and, on the margins, is accurate.