Economic agents obtain the goods and services they demand by paying the cost, that is, by spending. If we rewrite our aggregate expenditure function for an open economy, we get: AE = C + I + G + NX According to equation above, aggregate expenditures (AE) are the sum of consumption expenditures (C), investment expenditures (I), government expenditures (G) and net exports (NX). The aggregate expenditure function shows us the level of spending at each income level.