There is a hierarchy of relational structures involved in any rational inquiry. No step or stage of this hierarchy may be legitimately skipped, although in various contexts certain of them may be relatively invisible. As might be guessed by the title of this entry, that hierarchy is the one that runs between logic, principles, evidence and facts. In essence, this is a “meta-relation” between that which is universal – logic, that which is general (in the sense of genera) – principles, that which is specific (in the sense of species) – evidence, and that which is particular – facts. Now, anyone familiar with the works of Peirce and Dewey (see for example, HERE, HERE and HERE) will not find what I have to say in this post especially surprising. Nevertheless, the basic ideas presented seem like ones that deserve a broader audience than just and only scholars in American Pragmatism. And I have long found this litany – logic, principles, evidence, facts – to be a useful one, such that I am inclined to repeat it often enough that having a citable explanation will be of value.