Keynesian economics is a theory of total spending in the economy (called aggregate demand) and its effects on output and inflation. Although the term has been used (and abused) to describe many things over the years, six principal tenets seem central to Keynesianism. The first three describe how the economy works.

1. A Keynesian believes that aggregate demand is influenced by a host of economic decisions—both public and private—and sometimes behaves erratically.
2. According to Keynesian theory, changes in aggregate demand, whether anticipated or unanticipated, have their greatest short-run effect on real output and employment, not on prices. 
3. Keynesians believe that prices, and especially wages, respond slowly to changes in supply and demand, resulting in periodic shortages and surpluses, especially of labor.
4. Keynesians do not think that the typical level of unemployment is ideal—partly because unemployment is subject to the caprice of aggregate demand, and partly because they believe that prices adjust only gradually.
5. Many, but not all, Keynesians advocate activist stabilization policy to reduce the amplitude of the business cycle, which they rank among the most important of all economic problems.
6. Finally, and even less unanimously, some Keynesians are more concerned about combating unemployment than about conquering inflation.