On the other hand, whenever I turn my attention to the things themselves that I think I perceive very clearly, I am so thoroughly convinced by them, that I cannot help exclaiming: 'Let whoever can, deceive me as much as he likes: still he can never bring it about that I am nothing, as long as I think I am something; or that one day it will be true that I have never existed, when it is true now that I exist; or that perhaps two plus three added together are more or less than five; or that other such things should be true in which I recognize an obvious contradiction.'