Creation of causal graphs

Creation of causal graphs; in other words, how are causal graphs created? Where do they come from?

In all the examples I have seen, causal graphs are presented to the reader, sometimes with alternatives. It seems like the writer has some process for generating these graphs, but what is this process? Is it just human intuition?

The second problem of causal inference that Shalizi lists is "Given data about a system, find its causal structure". This seems to be the same question as asking where causal graphs come from. But he says this problem is harder than the first problem he lists ("Given the causal structure of a system, estimate the effects the variables have on each other"), and only goes into the first problem (he probably talks about the second problem as well, but I haven't read that far).

Morgan and Winship introduce a causal graph and then write: "suppose that these relationships are derived from a set of theoretical propositions that have achieved consensus in the relevant scholarly community" (p. 30). It's not clear what these "theoretical propositions" are or how the community came up with the relationships in the first place.

Pearl writes: "The sharp distinction between statistical and causal concepts can be translated into a useful principle: behind every causal claim there must lie some causal assumption that is not discernable from the joint distribution and, hence, not testable in observational studies. Such assumptions are usually provided by humans, resting on expert judgment. Thus, the way humans organize and communicate experiential knowledge becomes an integral part of the study, for it determines the veracity of the judgments experts are requested to articulate."

See also

• Methods of discovering causal effects