Can you have an economy without energy?

Neoclassical economics models output as a function of labour and capital — then discovers most of the growth it measures is explained by neither, and calls the leftover "total factor productivity": a polite name for we don't know. Keen, Ayres and Standish name it — it's energy.

Nothing is produced without it: labour is workers burning food, capital is machines burning fuel. Strip the energy out of a factory and the labour and capital sit idle — yet the textbook production function has no term for it. An economics that can't see energy can't see why growth stalls when energy gets dear, and can't cost a transition off fossil fuels except by guessing.

Put energy back at the centre and it changes. Open Goodwin with Energy or the reduced-form Iron Giants, push the energy constraint, and watch output respond the way real economies do — not the way equilibrium says they should.