Psychologists readily say that people can be involved in actions of unconscious defense in order to protect themselves against the threat of ambiguous thoughts and wishes. It is still not clear, however, to what extent one can say that in such cases people's behaviour is caused by mechanisms of defense functioning as specific mental devices. The concept of a mechanism of defense needs further clarification.

It is argued here that psychology may benefit from a tripartite distinction borrowed from Dennett's work on artificial intelligence (1978). This distinction may provide a better understanding of the explanatory power of the concept `mechanism of defense'. Following Dennett one can adopt the intentional stance, the design stance of the physical stance, in case one wants to understand and predict the behavior of people involved in unconscious, defensive acts.