Almost as soon as states began to rely upon revenues to carry on activities, those interested in fiscal problems became concerned about the importance and justice of the various sources of revenues. Bodin, the French scholar, gave one of the most interesting early classifications. He enumerated seven sources for securing public revenue which, he said, included all that could be thought of. They were: (1) landed domain; (2) conquests from enemies; (3) gifts from friends; (4) tributes from subject states; (5) public trading; (6) customs duties; (7) taxes.

Such a classification is interesting when compared with the important modern sources of revenue. Bodin held that the revenues from public domains were the most just and certain, but that customs duties were wholly just. His reason for the latter was the one commonly held at that time - if any foreigner was to gain by trading, let him pay for it. Taxes were only to be used when all other sources failed to produce a sufficient amount.

Adam Smith divided revenues into those coming from a fund belonging to the state, and from a fund belonging to the citizens. He was not in favor of the state entering industry, and believed that most revenues should come from the citizens. Most of the other early fiscal writers were likewise concerned about the important sources of revenues, and many of these sources were discussed, not only from the fiscal point of view, but from the standpoint of economic principle and ethics as well.