  Now it is true that the essence of Hesperus cannot be discovered by a mere thought experiment. That is because what makes Hesperus Hesperus is not the stereotype, but what underlies it. But it does not follow that no one can ever have access to the essence of a substance, but must always rely for identification on a fallible stereotype. One might think that for the person him or herself, while what makes that person that person underlies what is observable to others, it does not underlie what is experienceable by that person, but is given directly in their own self-awareness.