This week I've been given to study from my highschool teacher Descartes' Demon argument but I have several doubts I fully understand it ,but let me put this in clear order :
1) I understand that this argument is about whether we can have any knowledge at all about external world which includes existence itself .
2) The argument says that there exists an evil demon who is capable of deceiving us in the same way we suppose God to be able.
3) The argument is solved by the fact that if I am deceived it follows that I exist otherwise I can't be deceived.
Now my question concerns the third point:
How do I know that this evil demon is not feeding me the thought that "if I am deceived it follows that I exist " ?
My evil demon is so smart that he knows that giving me this thought I would think that I exist because I would have been able to think that.
But again how do I know that the demon is not again fooling me by feeding me the above thought ? I would think that I outsmarted him but he would be the smarter because he knows this and that's why he does this.
This can keep going for ever so it seems to me that I can never be sure of what I am thinking .
So the question breaks down to this :how do I know I am not still playing devil's game when I say that I must exist in order for this demon to deceive me ?