Standard Macro Model Intuition In the standard model of Aggregate Demand and Aggregate Supply which display equilibrium in all the markets, I often get confused on how a change in one variable will shift curves. Say, output decreases - how can one determine the causality between a change in output with other variables? 

For example, can prices change output and output change prices? What about other variables - GDP, interest rate?
Rule of thumb: if the changed quantity does not appear on an axis of the graph, its effect (if any) will be a shift of the curve, rather than movement along the curve.

For example, an AD-AS graph has price and quantity on the axes. Interest rate does not appear on the axes, so an increase in the interest rate (say) could be associated with a decrease in the money supply, resulting in a decrease in demand that shows up as a shift of the aggregate demand curve to the left.