Here are some additional fourfolds from philosopher Richard McKeon.
McKeon wrote much on the subject of rhetoric. A favorite fourfold of concepts was that of Things, Thoughts, Words, and Actions. He called these “commonplaces of inquiry” or “places of invention and memory”. Two rhetorical devices he used were amplification and schematization. Amplification can extend the scope of, for example, words to the other three, similar to the principle of indifference. “Objectivity is the inclusive principle of indifference by which it is recognized that being is grasped only in what we think, and say, and do about it.”  Schematization was used to identify and distiguish, for example, commonplaces. Thus I think amplification is a conjunctive device, and schematization is a disjunctive device.
Another fourfold of subjects by McKeon was Topics, Themes, Theses, and Hypotheses. McKeon wrote, “Speculation concerning discourse must avoid the fixities of categories, doctrines, methods, and assumptions which discourse assumes in any one form of philosophy or inquiry, if it is to include all the forms which discourse takes in philosophy and in inquiry, action, and production. This is possible because the variety of categories or elements is approached in discourse by way of common topics or ‘commonplaces’; the variety of facts or statements of what is the case by way of common hypotheses; the variety of arts or methods of treating problems by way of common themes; and the variety of assumptions or principles by way of common theses.” 
Are both these fourfolds aligned correctly with the previous Knowable, Knowledge, Known, and Knower? McKeon’s use of terms in his rhetoric was very fluid, perhaps to prevent systemization or to promote pluralism. However, his main reference to fourfolds was Aristotle’s four scientific questions, or Four Causes, which we can use to try to understand his fourfolds.
Theresa Enos (ed.) / Encyclopedia of Rhetoric and Composition: Communication from Ancient Times to the Information Age
 Richard McKeon / Selected Writings of Richard McKeon: Volume One: Philosophy, Science, and Culture
 Richard McKeon / Selected Writings of Richard McKeon, Volume Two: Culture, Education, and the Arts
H. L. Ulman / Things, Thoughts, Words, and Actions: the problem of language in late Eighteenth-Century British rhetorical theory
[*5.197, *6.140, *7.162, *7.165]