 To see the trajectory from earlier theories of mind, it will be helpful simply to see that, in the cogito argument of the First and Second Meditations, Descartes sees reason to doubt all features of his mind other than what is consciously available to him. And even then, his conscious thoughts serve only as evidence of his own existence—they don’t give any further evidence that what they represent about things external to him either exist at all or exist as represented by the idea in his mind. And so consciousness implicitly becomes, for Descartes, the “mark of the mental” and any further development of theories of mind along these lines will have to consider the role of consciousness in the mental economy.