Blackboard qualitative proofs of the "existence" of, say, an equilibrium between demand and supply - beloved of economists trained in the maths of the department of mathematics rather than the maths of the departments of physics or engineering - are meaningless because they don't tell how big is big.

Now being at present in woolly monkey mode, I could a tail unfold about this comparison between the mathematics of mathematics and the mathematics of physics, but that would distract from the main point.

Prudence, you no longer rule my world

is the title of an entertaining article in Times Higher Education by Deirdre McCloskey of the University of Illinois Chicago, in which she suggests reasons why leaving economic planning to the rocket scientists is bound to go haywire.

Warning: this article contains religious references, so if you are seriously allergic to religion I recommend you take some antihistamine before reading.  There isn't anything that should disturb a devout atheist, though.  But what she says does remind me of hearing something about economists who think that, because they can manipulate eigenvalues, they're the cat's whiskers.