Comment by mcswell

The edges are labeled by transitive verbs, where the arrow points from the subject of that verb to the direct object. (I'm counting particle verbs, like "leads to", as verbs.) The nodes are labeled by nouns. If you can change a noun to a verb, I guess you would be changing what is an edge and what is a node.

Example: In the article's first diagram, there is a node labeled "Innovation". This could be replaced by a node labeled "Capitalist" and a node labeled "Improvement", with an arrow from the first to the second labeled "innovates."

So yes, if you can replace a node by an edge (and vice versa, although I don't give an example), this node vs. edge thing is fuzzy.