not for profit bookkeeping The principle of rational investment: investment in securities investment in analysis and comparison. Two extremes can be envisaged. In an extreme case, each production is done by a single individual, such as a person making a car. In this way, the person is going to trade with a lot of intermediate goods suppliers, and also to trade with the demanders of their products. In this case, all transactions are conducted through the market in many individuals. In another extreme cases, all the production in the economy in a large enterprise, such as the complete car was produced in the enterprise interior, don't need to make any intermediate products trading market. Therefore, the same transaction can be conducted either through the organizational form of the market or through the organizational form of the enterprise. Companies exist, or companies and markets coexist, because some transactions cost less in the enterprise, while others cost less in the market.