The core Keynesian innovation has been to explain that an economy can be stuck in a crisis because of lack of demand, but there have been those that argue that this isn't possible in principle. The latter, implicitly or explicitly invoke some form of Say's law, arguing that supply creates its own demand.
For instance, here is an Austrian perspective:
Say’s ideas were used to settle a debate between the British economists David Ricardo and Thomas Malthus who believed recessions were caused by a general glut. The concept of a glut for a single good is easy enough to understand: there is more supply on the market than demand at the offered price. A glut can be alleviated by a fall in the price of that good. The producers of the good may take a loss if the market price is below their costs, but the market can always clear at some price.
The idea of a general glut is that all markets for all goods are in surplus. And for some reason, prices are unable to fix the problem.
Say's Law And The Permanent Recession | Zero Hedge


, the capital stock (K), or the labor stock (N).