Does the logical reductio ad absurdem still work given that the argument is an empirical one rather than a logical one?

Point taken – thanks. In fact, after that somewhat clumsy attempt at sarcasm I made much the same empirical argument as you did: it all depends. As you point out, we're not all paper pushers or penmen.

As regards the increased productivity argument I would add the ECON 101 dimension: if the 4-day workweek were as productive as it's made out to be successful firms would have introduced it already and the fuddy-duddies would have gone to the wall. Natural selection Schumpeter Hayek Ludwig von Mises and the American question: if you're so smart why aren't you rich ... etc. etc.

As regards the increased productivity argument I would add the ECON 101 dimension: if the 4-day workweek were as productive as it's made out to be successful firms would have introduced it already and the fuddy-duddies would have gone to the wall.

Having taught ECON-101, I'll also point out that (1) this argument assumes a complete network of perfectly competitive markets which (2) is nothing like what we have.

Firms are not productivity optimizers even in the traditional marginalist theory, they are profit optimizers, and there are many reasons why there can be productivity increases that are not reflected in increased profit for labor hour. Indeed, the massive departures we have to make from the real world in order to arrive at a model in which profit optimizing and productivity optimizing are equivalent should themselves signal that in general, they are anything but equivalent out in the real world.

Thanks for making the point (ECON 301?)

Second bash:

As regards the increased productivity argument I would add the ECON 301 dimension: if the 4-day workweek were as productive as it's made out to be successful firms might under certain circumstances have introduced it already and the fuddy-duddies might in some cases have gone to the wall and you can read all about the nitty-gritty in Samuelson's Economics 125th edition.

Is that OK now>? :-)