Brain in a Vat

Philosopher Descartes makes a bold proposition that the external incidents and internal thoughts we think are self-experienced is instead the result of manipulations by an all powerful evil demon. We are being deceived to think and act a certain way. What we believe, see, hear or feel are controlled by fate-- something bound to happen or sense because we are merely brains hooked on to a life-support machine. Our brains are fed with external memories, and ideas we never experience, are yet ours. "Life" would seem normal and reality-like, but everything that has happened or will occur is an illusionary happening. It is as if we are living in a seemingly reality-driven fantasy; however none of the things that transpire or occur is actually real.
What is described above obviously appears impractical and complicated. Before debating the validity of the brain in a vat hypothesis, we have to first distinguish between what are beliefs and knowledge and in addition comparing the truth and falsehood among them. In other words, what makes a belief and knowledge true or false? A belief is one's interpretation towards a proposition or simply personal perception. With regards to the beliefs you make, the validity and falsehood of that belief is flexible because your attitude governs whether it be true or false. However, the justification of the true or false beliefs is much complex. Justification needs evidence and reasoning. Possible examples of types of justified belief:
For the former, justified true belief is as followed: