I’m still failing to see the contradiction: is there anything I have said anywhere that contradicts your conclusion?

Therefore, any action which, over time, costs more than its utility cannot, by your own terms, be rational, Q.E.D.

I define rationality as ‘enhancing long-term net benefit’ (or well-being, or welfare, or any such notion). This can be restated as ‘[an action] not costing, over time, more than its utility’.

But let me try to clarify some of the points above.

I am confused by your use of the terms rationality and utility. For me, utility is merely a measure of the overall benefit experienced as a consequence of a transaction. It is possible to envisage an infinitely large utility, both positive and negative, so there are, in effect, no bounds to this.

I am not sure how dividing utility by cost produces a meaningful value. I would subtract these two quantities. If the difference is positive, the behaviour involving the transaction was rational; if it is negative, it was not. (I don’t think arguing about what exactly zero means makes much sense, since it is not really possible to establish either cost or utility with any accuracy.)

I prefer a scale of 0 to 1, ranging from zero utility to maximum utility.

Do you see rationality as a continuous variable, rather than a boolean? For me it is the latter — a behaviour or a choice is either rational (if it enhances overall long-term wellbeing, i.e. the overall utility > the overall cost), or it is not (if it decreases overall long-term wellbeing, i.e. overall utility < overall cost).

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