The facts that I cannot then do something else with my car, cauliflower, or time does not stop the side by side comparison of NOT trading with trading from being a Pareto improvement in any of these cases.
Agreed, although novalis, fortyeridania & I are referring to externalities rather than personal opportunity costs. And if I start taking every esoteric kind of externality into account, it’s pretty hard to think of a trade that doesn’t exert ripple effects through them.
I have a Dodge Charger and would rather have a plymouth fury. You have a plymouth fury and would rather have a dodge charger. We trade. That is a Pareto improvement.
A novalis/fortyeridania-type reply here would presumably be that the trade means I no longer buy a Charger and/or you no longer buy a Fury (or substitutes for those), which is the same kind of externality as if I no longer buy a watermelon because I found one. (A similar argument applies if instead of trading, at least one of us sells our car and buys something with the money.) That kind of argument seems to apply to nominally Pareto-improving trades in general, although I’m not sure how seriously to take it.
Agreed, although novalis, fortyeridania & I are referring to externalities rather than personal opportunity costs. And if I start taking every esoteric kind of externality into account, it’s pretty hard to think of a trade that doesn’t exert ripple effects through them.
A novalis/fortyeridania-type reply here would presumably be that the trade means I no longer buy a Charger and/or you no longer buy a Fury (or substitutes for those), which is the same kind of externality as if I no longer buy a watermelon because I found one. (A similar argument applies if instead of trading, at least one of us sells our car and buys something with the money.) That kind of argument seems to apply to nominally Pareto-improving trades in general, although I’m not sure how seriously to take it.
I don’t think those are not externalities, they are changes in opportunity.