That's because of the nontrivial math. It will be found in general equilibrium section toward the end of introductory microeconomics, or at the beginning of a g

That's because of the nontrivial math. It will be found in general equilibrium section toward the end of introductory microeconomics, or at the beginning of a graduate course in macroeconomics. Page 182 of this excerpt from Acemoglu's Economic Growth discusses aggregation and the possibility of a representative household. http://users.econ.umn.edu/~guvenen/DaronBook1.pdf http://users.econ.umn.edu/~guvenen/DaronBook1.pdf Aggregation of firms (and production functions) works quite nicely theoretically. Unfortunately, the same is not true for household / demand aggregation. The Debreu-Mantel-Sonnenschein Theorem aka. the "anything-goes" theorem gives a stark negative result. Utility functions are just too idiosyncratic to aggregate in every possible case. However macroeconomists still do this for purposes of tractability. We know that sometimes aggregation is possible, if utility functions take certain forms. This is only one of many dimensions modern macroeconomic models are far from realistic. This is no secret to anyone.