It is argued that two major symptom dimensions underlie common mental disorders. These are depression related symptoms on the one hand, and anxious symptoms on the other. Each of these symptom dimensions is relate to a set of social variables, but an individual patient may have social factors present that are associated with each symptom dimension, thus producing an overlapping of symptoms. Another reason why the symptom dimensions overlap is that depression and anxiety relate to reward and punishment systems respectively, and these systems are necessarily reciprocally related to one another. Finally, each of these systems is related to abnormal activities in both nor-adrenergic and 5-hydroxytryptaminergic neurones. It is argued that in order to produce a useful model for common disorders one should distinguish between three groups of factors: those producing vulnerability to anxious or depressive symptoms, those factors releasing symptoms at a particular time, and those factors which determine how long illness lasts. These three groups of factors are respectively called vulnerability, destabilisation and restitution.