A philosopher named Alvin Plantinga develops the notion of warranted beliefs over a three-book series, culminating in Warranted Christian Belief. His goal, very briefly, was to establish how we know the things we know, and what counts for certain knowledge.
One of his central concepts is that of a “properly basic belief.” This is a kind of belief which everyone understands, and very few think much about.
Consider the medium through which you are reading these words; say it is through a book. Upon recognition of the book, you immediately and unreflectively believe that there is, in fact, a book in your possession. Say you heard your daughter calling your name: As soon as the sound reached your ears, and the message reached your mind, you would immediately and unreflectively believe that she had spoken your name.
These things seem obvious, which is the point – such beliefs Plantinga regards as properly basic, because they are the fundamental beliefs of our existence. In these instances, we simply trust the deliverances of our senses without a second thought – in fact, without a first thought, which is what makes them basic.
What is the expected objection here? Well, it is possible that there really isn’t a book in your hands, after all! Likewise, how do we know your daughter is not a figment of your imagination? What if we’re all in the Matrix, and none of this actually is real?
On the one hand, if you want to doubt absolutely everything, have at it! But you will only be left with your own existence, and it seems irrational to believe that you exist alone, that absolutely everything else around you is simply imagined by you. (This could be demonstrated at length, but I will presume we share a position against such a view).
On the other, once Neo breaks out of the Matrix – how does he know he’s out?
Well, by his senses and other properly basic beliefs. All in all, he forms all of his beliefs in essentially the same way he did while in the Matrix. In fact, his basic beliefs were required in order to break out of the Matrix!
It occurs to me that this is like the law of noncontradiction. The law is so fundamental that when you set out to prove it false, you realize that you can only do so by assuming it true. The dog catches his tail, but he cannot consume himself.