a system in which a multiplicity of factors may weigh in at once, not just in a line and one at a time; a system, then, in which our feeling, for example, that "Robert is prompt," will proceed from our understanding of the totality of his nature, rather than from a coded set of properties pried from his personality; … [William H. Gass, "The Story of the State of Nature," p. 134]"Robert being prompt" is a consequence "caused" by various particular inputs, as the system sees or defines them, and a system of rules or linkages that produce given consequences from those particular inputs. The key to explaining why Robert is prompt in some particular case is a matter of laying out, as best we can, the system of connections that Robert is such that given certain circumstances we can predict that he would be be prompt.
According to Peirce, however, this is only one of three possibilities. Besides seeing Robert being prompt diagrammatically, we could see it in terms of an image. This is what Gass calls "a coded set of properties" attaching to him as various external characteristics. Such external characteristics could be "pried from his personality;" others could be photographed; the key is that they are external characteristics of Robert. The system of such properties or relationships can be represented diagrammatically, but Robert an opaque node or a dimensionless point, a empty terminus of some and not others of those relationships.
The third possibility, which is historically probably the first and epistemologically the most common, is to understand Robert metaphorically. If we can find a system that is similar to Robert, that as Peirce puts it runs "parallel" with Robert, we can use that to explain things like Robert being prompt. For instance, I might compare Jack to a Prussian officer, or to the Pony Express where promptness was a virtue. The biggest problem with metaphors is a lack of acquaintance with what is supposed to be the known side of the metaphor. Comparing Jack to a Prussian officer does me no good for the simple reason I don't know any Prussian officers. To remedy this, I might even compare him to myself. But to the extent I can discover increasing similarities with something I do know, I come to an increased understanding of Jack.
Gass overall, I think, is lamenting the demise of metaphorical understanding, of art. I, in turn, would lament the demise of diagrammatic thinking. We live, at least publicly, in an age of images, where the system of external relationships is the reality and the human being is no more than an empty point of reference in different images. We can still think diagrammatically and metaphorically in private, through philosophy and art such as it is these days, but then that privacy is increasingly under siege as well.