What do we know and not know about macroeconomics?

My coauthor and I are currently revising our economics textbook ¡ª one of our decisions is to emphasize the Great Recession and the pandemic over the Great Depression ¡ª so I might be expected to have an answer to this question. Instead, standing on one foot, I would like to offer a short primer to guide us through future crises and downturns.

Let¡¯s start with what we don¡¯t know.