Allgemeine Theorie der Beschäftigung, des Zinses und des Geldes
John Maynard Keynes, in 1936, proposed the psychological law in his work: "The General Theory of Employment, Interest and Money". The law basically captures and understands the essential spending behavior of the household sector. Keynes uses the term 'psychology' in his law but the law is just a basic observation of consumer behavior and consumption.