 Nichols and Stich (2003) employ a model of the mind on which having a propositional attitude such as a belief or desire is a matter of having a representation stored in a functionally-defined (and metaphorical) “belief box” or “desire box” (see also the entries on  belief  and  functionalism).  On their account, self-awareness of these attitudes typically involves the operation of a simple “Monitoring Mechanism” that merely takes the representations from these boxes, appends an “I believe that …”, “I desire that …”, or whatever (as appropriate) to that representation, and adds it back into the belief box. For example, if I desire that my father flies to Hong Kong on Sunday, the Monitoring Mechanism can copy the representation in my desire box with the content “my father flies to Hong Kong on Sunday” and produce a new representation in my belief box—that is, create a new belief—with the content “I desire that my father flies to Hong Kong on Sunday”. Nichols and Stich also propose an analogous but somewhat more complicated mechanism (they leave the details unspecified) that takes percepts as its input and produces beliefs about those percepts as its output.