Will, Dubitability

As Sartre, notably, emphasizes, what Descartes asserts is not 'I doubt', but 'I can doubt'. Hence, what he establishes as indubitable is not that he doubts but that he can doubt. Now, an ability to doubt entails an ability to consider that a situation is otherwise than it is given to be, which entails an ability to modify the situation, e. g. that one may be dreaming entails that one can wake up and discover oneself to be lying in a bed, and to be not sitting in a chair in front of a fire. So, Descartes' 'method of Doubt' entails Will, i. e. an ability to change a given situation.