In the last two Chapters we have discussed and illustrated some of the basic forms which the interrelationships between the variables in a dynamic economic system may take. It is now necessary to consider what the general structure of these interrelationships will be like in an actual economy. For this purpose we must consider a complete, but simplified, set of relationships which cover simultaneously all the main markets in the economy (i.e. a macroeconomic model) rather than the relationships in one single market in isolation from the rest of the economy (i.e. a micro-economic model).