Which economist introduced the term 'animal spirits' to describe emotional influences on confidence?

John Maynard Keynes introduced the term “animal spirits” to describe emotional influences on confidence. He used it in his 1936 book, The General Theory of Employment, Interest and Money, while explaining why economic decisions cannot always be understood as purely rational calculations.

For Keynes, animal spirits referred to instincts, optimism, pessimism and other psychological impulses that shape people’s willingness to consume, save or invest. Business investment is especially sensitive to confidence because companies must make decisions about uncertain future returns. When optimism rises, investment and hiring may increase; when fear spreads, spending and production can weaken.

The phrase did not originate with Keynes. Earlier writers, including Thomas Hobbes and Isaac Newton, used “animal spirits” in philosophical or physiological contexts. Keynes adapted the expression to macroeconomics, giving it its modern economic meaning.

A common mix-up is attributing the concept to behavioral economists George Akerlof and Robert Shiller. They popularized and expanded the idea in their 2009 book Animal Spirits, but Keynes introduced its influential economic usage decades earlier.