The total amount of real goods and services that the enterprises in an economy are willing to provide at any given ratio of prices to wages. This can be increased by greater productivity due to increases in the volume of productive equipment or improvements in technical knowledge or the quality of the labour force. Whether actual output equals aggregate supply depends on two conditions. First, there must be sufficient aggregate demand to match the supply: if there is not, output is demand-constrained. Second, there must be a sufficient supply of labour to satisfy firms’ demand for it: if real wages are low, aggregate supply by firms may require more employment than the labour supply forthcoming at these wages, in which case output is constrained by labour shortages. In an economy where firms do not act competitively, the concept of aggregate supply is not applicable: firms in markets characterized by imperfect competition do not have supply curves. See also demand-determined output.