> A flat tax is regressive [because what matters is utility of money]. It's fine to think that, but normally when people are talking about tax progressiveness,

> A flat tax is regressive [because what matters is utility of money]. It's fine to think that, but normally when people are talking about tax progressiveness, they are thinking about the fractional tax on dollars, not "utils". Otherwise, you'd also call our existing, progressive taxation scheme "regressive," since it still probably taxes poor people's utils at a higher rate than rich people. And there would probably not anywhere in the world be a tax scheme that can properly be called progressive. One good rule of thumb, IMO, is that when you want to change the meaning of a classifier such that all extant instances of the classified type fall into a single bucket, that's probably not a useful change. YMMV.