Says Law#

Jean-Baptiste Say’s 1803 book, Treatise on Political Economy.

The income generated by past production and sale of goods is the source of spending that creates demand to purchase current production

The buyer must first have produced something - it is not money itself that is the source. Merely handing out money is not good as nothing has been produced.

https://www.investopedia.com/terms/s/says-law.asp

Theory of Revealed Preference#

Paul Anthony Samuelson in 1938.

States that consumer behavior is the best indicator of their preferences - not what they say.

It can be broadened to anything. Do not beleive what anyone says - verify by observing what they do.

https://www.investopedia.com/terms/r/revealed-preference.asp

The Cantillion Effect#

https://www.adamsmith.org/blog/the-cantillion-effect