 As a brief aside, some authors use neuron diagrams like these as representational tools for modelling the causal structure of cases described by vignettes. So, they might say that the neuron b represents whether Suzy is aggrieved, a represents whether Suzy throws a rock at the neighbor’s window, and e represents whether the window shatters. Hitchcock (2007b) gives reasons to worry about this use of neuron diagrams, and argues that we should instead use causal models as a representational tool (see the entry on  causal models,  and  §3.2  below). Whatever we think about using neuron diagrams to represent the causal structure of scenarios described in vignettes, there should be little objection to using them to model systems of neurons, hooked up with stimulatory and inhibitory connections in the ways indicated in the diagram (Hitchcock 2007b agrees). That’s how neuron diagrams will be understood here. So the neuron diagram isn’t being used to model Suzy and Billy’s situation. It is used to model a very simple system of five neurons, and, arguably, the system of neurons has a similar causal structure to the vignette involving Billy and Suzy.