This paper attempts to define the areas of applicability of behavioural and mentalistic explanations of neurotic behaviour. It is argued that intentional behaviour requires mental concepts for its explanation on the grounds that the statement of reasons which form the basis of intentions cannot be submitted to a stimulus-response analysis. This argument applies to situations in which the therapist uncovers the reasons for purposeful action of which the agent may initially be unaware. It is further argued that behaviour of this kind is rule-conforming and not law-abiding and therefore is not susceptible to explanations of the kind that are available in other areas of science. It is nevertheless argued that causal explanations can be given in terms of reasons for action.