8 principles re: public purpose of taxes

Here are eight (8) important principles regarding the public purpose of taxation.

[1] Tax revenues must never be used for purely private purposes.
[2] Tax revenues must never be used for the exclusive benefit of private persons.
[3] Singling out a particular class for taxation is allowed as long as there is valid classification.
[4] Congress enjoys the power to select the subjects of taxation and it is not required to impose the same tax to everyone or everything.
[5] However, equal protection of the laws still applies. Hence, the law must apply to all members of the same class, there must be substantial distinction that makes real differences, the differences must not be confined to existing conditions only and the distinction must be germane for the purpose of the law.
[6] There is no constitutional requirement that a taxpayer get direct benefit from the tax he pays.
[7] The public purpose of taxes is not only a determination of whether the function is ministrant or constituent in nature. The ever-changing complexities of human life and increasing social challenges, the meaning of "public purpose" has changed. It has adopted a modern meaning.
[8] The public purpose of a tax law must exist at the time of its enactment.