Is this real?
Am I sitting at my desk, composing, typing and indulging my caffeine addiction?
Or as Descartes considered as a distinct possibility, am I being deceived by malicious demon?
Personally I’m inclined towards the former, but that’s not enough, I need to be able to support my position somehow.
To attempt this lets first look at what lead Descartes to entertain this possibility.
His motto is doubt everything, by doing this he is trying to find some truth that is absolutely indubitable; the possibility that all his senses are unreliable is just one stage in the process.
His reasoning is more or less as follows: My senses sometimes deceive me I could be dreaming or delirious, the fact that I think I’m seeing something is no guarantee that it’s real. As a result of this we can never be sure if what we perceive is real. The evil demons influence is offered as a reason for why this might be.
Now there’s one fairly obvious flaw with this argument, which is that he’s appealing to his senses to argue that senses are unreliable. How could you be sure that your dreams weren’t real unless you were comparing them to real life.
So can we be sure we’re not being deceived?
No, we can’t, but the inability to disprove an assertion is no reason to accept it as truth. If I told you there was an invisible fairy living in my laptop altering my files when no ones looking, you wouldn’t be able to disprove me, but that’s not a good enough reason for anyone to take the claim seriously.
It’s possible there’s a malicious demon deceiving us, but highly improbable.