And finally we have justification. Justificatiton is basically having some sort of legitimate evidence to support my belief. And justification can come in a variety of forms. Most often, it comes about through testimony. That is taking someone’s word for it.In fact most of what we know about the world was learned through testimony. We took our teachers’ word for it when they were teaching you stuff, and the same goes for every book you’ve ever read and every news report you’ve ever seen. They’re all just forms of testimony, which you accepted as justification for your knowledge and your beliefs. But justification can come in other forms. Another common type information you acquire through your senses. If I believe that a book is a book, because I already beliefs about books such as their shape and physical properties. Then, having had extensive experience with them in the past, I’m identifying the book as a book through my direct contact with it. It looks, feels, acts like a book therefore it is a book.
So, I now have knowledge that the book on my table is a book because I first believe it’s a book and also it is in reality a book, that is, my belief corresponds to reality and is therefore true.
This was the consensus for a while until an American philosopher Edmund Gettier came along in the 1960s. He began to question this definition of knowledge and created what are known as Gettier cases. Say a person wants to know what time it is and they look at the clock on the wall which clearly shows the time as 3 o’clock. Looking at the clock is a reasonable way of telling time so they have a justified belief. However, they don’t know that the clock is broken and its hands haven't moved in days but by chance it is exactly 3 o'clock right now. Does the person actually know the time as he looks at the broken clock. Back in 1948, Bertrand Russell used this case to illustrate the possibility of true belief without knowledge. Many claimed that Gettier disproved the justified true belief definition of knowledge.
So where does this leave us? We don’t have a conclusive answer to how do we know what we know.
But I’m now going to try to explain how we know that we know stuff or in reality, explain why we can’t. Philosphers like Hume and John Locke both presented ideas of scepticism. To explain sceptiscim, its best to use examples. One of the examples was the Dreaming argument. The ancient Chinese philosopher Duan Chu once dreamt that he was a butterfly and began to worry that he did not know whether he was a man dreaming he was a butterfly or whether he is now a butterfly dreaming he was a man. If what you are now experiencing is just a dream then it's not clear that you know anything about your immediate environment or even about yourself. The 17th century philosopher Rene Descartes, however, suggested that even if you are dreaming you should still be able to know that a square has four sides or that two plus three equals five. But Descartes found a way to raise scepticism about those facts too. He said that it feels natural to us to make those simple mathematical judgments but pointed out that we could ask ourselves whether what feels natural to us really has to be true. Descartes developed a powerful sceptical scenario designed to make you doubt everything including your grasp of abstract facts. It has been updated for the modern world and now goes like this. Imagine a brain kept alive in a vat, and connected to a supercomputer that delivers signals to simulate the experience of reality. The computer program is good enough that the brain-in-a-vat experiences a perfectly realistic virtual world. Is there anything you could point to, in your present experience, to prove that you aren't a brain in a vat? Sceptics don't try to prove that you actually are a brain in a vat, they will argue instead that it's bad enough that you just might be, but you can't tell the difference. You can't prove you aren’t the brain in the vat and your inability to rule it out means that you don't actually know anything.
So scepticism is a huge problem in answering this question. We can’t truly know anything if we don’t know what reality we are in, if any reality at all. Now the very problem with scepticism is its difficult to argue against, so the only way to truly undermine it is to engage in a form of pragmatism. Thomas Reid was a key philosopher in questioning people like Hume’s scepticism. Here is a quote from ‘An Inquiry into the Human Mind’. "what is the consequence? I resolve not to believe in my senses. I break my nose on a post that comes in my way; I step into a dirty kennel; and, after twenty such wise and rational actions I am taken up and clapped into a mad-house.” Reid is basically suggesting that it is in our best interest to just assume there is an external world, to think otherwise would be mad. He agrees that Hume and Locke have arguments, but that those arguments should be first founded on common sense. If there is a battle between common sense and philosophy, it should be philosophy who makes room, because to discount our common senses is to throw away everything we know about reason and perception. We need common sense to ground our ideas and allow us to function daily without questioning our very move. Modern day philosophers such as David Rorty are strong proponents of ruthless pragmatism towards philosophy.
The truth is we will never truly understood how we know what we know, and how we know that we know it because we can never truly understand the world we live in. We could all be figments of my imagination, or a simulation of a superior being, but whats the fun in living life like that. This leaves us questioning why do we do what we do everyday, why do any work if we’re just a simulation, or get out of bed in the morning. Philosophy is meant to help us not hinder us , and sometimes question like this can never be truly answered.