Oskar Lange, a Marxist economist, studied and adapted the ideas of non-Marxist economist John Maynard Keynes. Lange played a key role in merging Keynesian and pre-Keynesian economic theories, which influenced macroeconomics for decades. He focused on interpreting Keynes's General Theory and adjusting it to his own beliefs about money, saving, and investment. Lange's main disagreement with Keynes was not about macroeconomics, but rather about econometrics.