Systems

If by 'system' is meant — and this is the minimal sense of the word — a sort of consequence, coherence and insistence — a certain gathering together — there is an injunction to the system that I have never renounced, and never wished to. … 'System ', however, in a philosophical sense that is more rigorous, and perhaps more modern, can also be taken to mean a totalization in the configuration, a continuity of all statements, a form of coherence (not coherence itself), involving syllogicity of logic, a certain syn which is no longer simply that of gathering in general, but rather of the assemblage of ontological propositions.

— Derrida and Ferraris, I Have a Taste for the 

Secret, (Polity Press, 2001), p. 3

Diagrammatic thinking, at least as I envision it, is also an effort to get away from the "system" as an axiomatic, analytically formal, would-be universal "totalization" and to see it as a particular collection of indices and relationships abstracted from experience on the one side and limited in its applications to that kind of experience on the other.

And, such "systems" occur on much simpler levels still. Andrew Whiten's "intervening variable":

Andrew Whiten, "Triangulation, Intervening Variables, and Experience
Projection," Behavioral and Brain Sciences 21 (1) (1998):133

performs the same mediating function in what he calls the "triangulation" of patterns on the one side with consequences on the other.  It really doesn't matter exactly what the intervening variable is — whether it's a word, an image, or a layer of neurons.  What matters is that it's operating diagrammatically with "a sort of consequence, coherence and insistence — a certain gathering together."