Imagine that your brain is submerged into a vat and it is connected to a computer, which gives you a world made by a group of crazy scientists. You feel this world is as real as your existence. This is a thought experiment proposed by Jonathan Dancy on his book “An Introduction to Contemporary Epistemology”, though this topic has been analysed by philosophers from Plato to recent ones.
Some people who have tried to comment this, state that the experiment is not clear because if the brain said “I am a brain in a vat”, it knows that it is in the real world. However, it doesn’t receive senses from that world, from the true world. Then, the sentence becomes illogical and false, showing the importance of language.
Other people support that this experiment confirms the inability of the brain to know the reality around us. The brain only feels some sensations from outside, besides a great part of it is removed when it processed. Then, we are doomed to search a little part of the reality.
“Brain in a vat” presents how the brain lies to us and how language is vital for us. The experiment teaches we should be honest and humble when we try to defend anything and we must see the world in the eyes of the rest of people. It is so representative that it has been recreated by science-fiction writers and film-makers, for instace, Matrix.
You can read it more detailed on the Wikipedia.