This paper argues that specific phobia is an ideal kind of psychiatric disorder because it bears the marks of a mature medical diagnosis and is amenable to causal explanation. A new and ambitious program of ‘causal revolution’ has recently emerged in psychiatry that hopes to refurnish our taxonomies by discovering the underlying biological and psychological causes that create and maintain mental illness. I show that the sort of causal story envisioned by the program is a mechanistic property cluster (MPC) structure, (...) which involves a causal mechanism that explains the co-occurrence of a disorder’s signs and symptoms (Kendler, Zachar & Craver, 2011). I then build a model of fear in humans and sketch a novel account of specific phobia as a configuration of the fear system in thrall to deregulated network dynamics such as hysteresis, tipping points, and feedback loops. Specific phobia has an MPC structure. I close by reflecting on whether we can reasonably expect other mental disorders to fit an MPC mold, and thus lend themselves to future causal validation. This paper shows that specific phobia holds a unique place in our picture of mental disorder that has so far been missed. It is an ideal kind of psychopathology. (shrink)