In the fields of epistemology and philosophy of mind it is said the first person (the subject, the self) has privileged access to his own thoughts. This implies the subject has access to (and knows) his own thoughts (has self-knowledge) in such a way that the third person (others) do not. Privileged access can be characterized in two ways:
The still prevailing traditional position argues each of us do in fact have privileged access to our own thoughts. Descartes is the paradigmatic proponent of such kind of view (even though "privileged access" is an anachronic label for his thesis):
For Descartes, we still have privileged access even in the doubt scenario. That is, for him we would retain self-knowledge even in those extreme situations in which we can't have knowledge about anything else.
Gilbert Ryle, on the other hand, maintains a diametrically opposed view. According to the radical behaviorism of Ryle, each of us knows our own thoughts in the same way we know other's thoughts. We only come to know the thoughts of others through their linguistic and bodily behaviors, and must do exactly the same in order to know our own thoughts. There is no privileged access. We only have access to what we think upon evidences supplied through our own actions.
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