Chapter 22 on fiscal policy should be read with some care.  The concepts are important, but the technical details of the chapter can be seen as merely extending the material of ch 20 to include taxes and government spending.  Note that the multiplier works the same as before for spending changes, but for tax changes a different "tax mulitiplier" applies.  The essence of the chapter is that total demand (aggregate expenditure) in the economy can be manipulated via the government's budget.  Therefore, in Keynes' view, if the economy were to be sluggish, the AE could be stimulated through tax cuts or government spending increases, and if the economy were to be "overheated", tax increases or government spending cuts could be used as contractionary measures.

The supplementary material, below, helps clarify the multiplier relationships dealt with in the chapter.