The first stage of Friedman's attack on Keynes was his effective though somewhat slippery critique of the idea that monetary and fiscal policy can be… - Paul Krugman

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The first stage of Friedman's attack on Keynes was his effective though somewhat slippery critique of the idea that monetary and fiscal policy can be actively used to smooth out the business cycle. Friedman argued that such active policy is not only unnecessary but actually harmful, worsening the very economic instability that it is supposed to correct, and should be replaced by simple, mechanical monetary rules. This is the doctrine that came to be known as "monetarism."