This document discusses the effectiveness of fiscal policy in controlling inflation or deflation based on the slope of the IS curve. It explains that fiscal policy will be more effective when the IS curve has a steeper slope (is less elastic) as it will allow a change in fiscal policy to more significantly impact the level of income and interest rates without crowding out private investment. It also discusses how the slope of the LM curve and positions of the IS and LM curves impact the fiscal multiplier.