@SteveRoth yeah. economics really confuses itself on this point. 1/

@SteveRoth economics gets, in general, that in nearly all interesting cases, an interior solution will prevail. whatever the good that comes with increasing some variable, some tradeoff will eventually arise and overwhelm it. 2/

@SteveRoth but then the very heart of modern economics is "utility maximization", which *by construction* has no interior solution. it is not a thing in the world, or even a model that tries to describe a thing in the world. it is just a gadget we've invented to organize how we explain and predict human behavior. 3/

@SteveRoth but our weirdly constructed little model bleeds into implausible attitudes about real phenomena in the real world. 4/

@SteveRoth we model utility as an increasing function of what we call consumption, so that consumption maximization takes on the unboundedness without tradeoff of utility maximization. 5/

@SteveRoth but that can only work is we let the modeled phenomenon stand-in for the thing in the real world. like "investment" and "saving" and all the rest, we easily confuse ourselves with false friends, drawing inferences from the models about things to which we give the same name but are in fact not well characterized by the model. /fin