Irving Fisher on main causes of boom and bust: over-indebtedness and deflation

19. I venture the opinion, subject to future evidence, that, in the great booms and depressions, each of the above-named factors has played a subordinate role as compared with two dominant factors, namely over-indebtedness to start with and deflation following soon after; also that where any of the other factors do become conspicuous, they are often merely effects or symptoms of these two. In short, the big bad actors are debt disturbances and price level disturbances.

While quite ready to change my opinion, I have, at present, a strong conviction that these two economic maladies, the debt disease and the price-level disease (or dollar disease), are, in the great booms and depressions, more important causes than all others put together.