In the Preface to the second edition of his book "General Systems Theory" Ludwig von Bertalanffy speaks of the "domains" of systemics, and briefly describes them as the Theory, the Methodology and the Philosophy of Systems. We have improved on this scheme by adding a fourth domain - Application - and rearranged the order in a more rigorous fashion. So the four domains of systems are Philosophy, Theory, Methodology and Application, interelated as an interpenetrative integral whole.
This model of the whole of systemic inquiry has two interrelated aspects, Knowledge and Action. Knowledge, in turn, is both philosophical (general) and theoretical (specific), while Action is both Methodology and Praxis. The primary action is that of a emerging process, so there is a movement from one to the other, and the progression of action is the spirial as we continually arrive at where we began, only a bit wiser. Inquiry proceeds from an inquiry into general principles to specific applications and from these to applicable methodologies designed to actualize itself as a whole. From this direct experience, we then return to general principles and iterate the process. (Banathy 1996)
The essense of the whole of systemic inquiry of the four is Knowledgable Action. Compare to "Enlightened Doing."
Keywords: Relationship, organization, feedback, resonance, harmony, complementary, emergence, relationship, elements, experience, action, wholistic, wholismic
Note. This Tetradic scheme is just one way of looking at it, and not intended to regarded as the only way. Triadic, Dyadic and Monatic schemes are also used, but the tetronic involves all of them.
This fourfold scheme is not new.
For example, the Native American scheme called the "Medicine Wheel" is based on "the Four Directions" aka, the Four WInds. See http://www.newciv.org/ISSS_Primer/4winds.html
Buckminster Fuller also conceived of a "Tetraheadron" four catagorical points in space, which he considers the minimal three dimensional structure. See http://www.cruzio.com/~devarco/index.htm for a wonderful introduction of Fuller
See also a detailed discussion of fourfoldness by Anthony Judge http://www.newciv.org/ISSS_Primer/fourfold.html