In respect of those truths I have no fear of the arguments of the Academics.  They say, 'Suppose you are mistaken?' I reply, 'if I am mistaken, I exist.'  A non-existent bring cannot be mistake; therefore I must exist, If I am mistaken.  Then since my being mistaken proves that I exist, how can I be mistaken in thinking that I exist, seeing that my mistake establishes my existence?  Since therefore I must exist in order to be mistaken, then even if I am mistaken, there can be no doubt that I am not mistaken in my knowledge that I exist.  It follows that I exist, I also know that I know. 

And when I am glad of those two facts, I can add the fact of that gladness to the things I know, as a fact of equal worth.  For I am not mistaken about the fact of my gladness, since I am not mistaken about the things which I love.  Even if they were illusory, it would still be a fact that I love the illusions.  For how could be rightly blamed and forbidden to love illusions, if it were an illusion that I loved them?  But since in fact their truth is established, who can doubt that, when they are loved, that love is an established truth?  Moreover, it is as certain that no one would wish himself not to exist as it is that no one would wish himself not to be happy.  For existence is a necessary condition for happiness.