1. give up one thing for getting another, the first principle of economics .
2. alternate
eg1: in modern society, there is one tradeoff between a clean environment and a high income, another between efficiency and equity .
eg2: there is always a tradeoff between inflation and unemployment, when reducing inflation , a short-term rise in unemployment appear. Why? Because prices cannot be adjusted immediately after reduction of money printed. When reducing the quantity of money, the prices remain high, then people reduce their spend, firms also reduce the quantity of their products, thus causing firms to fire workers. But all these would be temporary, after several years prices would be fully adjusted and then the unemployment would go down. Government also can use some policy instruments to control this short-term unemployment, such as reducing government spend, reducing the taxes.