To contribute (about money):
The useful and fair virtue: give some money in order to carry out a virtuous project for which one has a more or less direct interest, what a tax can organize in some cases (knowing this one can bring some returns). For instance, in the case of a virtuous work of which one knows that it will be useful for the state, but which by its character is not being sold directly to the public in a quantity representing its merit (not commercial), public who nonetheless will benefit from it more or less directly, it is true in this case a tax can be organized in order to reward the merit of the one (or those) who has (have) produced this work.
The useless and unfair vice: the same thing for a vicious project. For example: in order to make lose confidence to those who deserve more.