Inspired by philosopher Richard McKeon, I believe that philosophy as a whole is encompassed by four main philosophical stances, exemplified by four ancient philosophers: the Sophists (as a group), Democritus, Plato, and Aristotle. Their four systems of thought lay out principal philosophical directions, much like the compass directions east, south, north, and west lay out a complete set of primary directions.
Of course the compass directions can be subdivided into north-east, or south-south-west, and so on, and similarly each of these philosophical systems can be divided into four parts. This division into a four-by-four matrix is called the Archic Matrix and was written about at length in the separate but complementary works of Walter Watson and David Dilworth.
Watson and Dilworth described the four main philosophical directions to be perspective, reality, method, and principle: perspective for the Sophists, reality for Democritus, method for Plato, and principle for Aristotle. I have written about these philosophical perspectives previously in several ways.
Thus philosophy as a practice goes around and around and revisits the same ideas over and over. Perhaps McKeon thought his philosophical system followed in the footsteps of Aristotle, and probably Watson and Dilworth had a similar view.
Likewise, I believe that my fourfold of Structure-Function represents these four philosophical directions in the following way: Action(s) for the Sophists, Part(s) for Democritus, Structure for Plato, and Function for Aristotle.