A public office is a public trust.The incumbent has a property right in it, but the office is conferred, not for his benefit, but for the benefit of the political society. The duties imposed upon the officer are supposed to be capable of classification under one of three heads: the legislative, executive, or judicial; and to pertain, accordingly, to one of the three departments of the government designated by these names. But the classification cannot be very exact, and there are numerous officers who cannot be classified at all under these heads. The reason will be apparent if we name one class as an illustration. Taxing officers perform duties which in strictness are neither executive nor judicial, though in some particulars they merely execute the orders of superiors, and in others they judge for themselves what is to be done. But sometimes, also, their duties partake of the legislative. All such officers are usually called administrative, while inferior executive officers are designated ministerial.
Cooley, Thomas M. "Liability of Public Officers to Private Actions for Neglect of Official Duty." Southern L. Rev. 3 (1877): 531-52.