Although these definitions seem totally different, it is often difficult to distinguish between “what we truly know” from “what we believe to be true”. This is because we never have the time, skills, materials and will to carefully check every single thing in life, so we have to rely on information supplied by others. Also, human process of learning is really very effective for survival in the warm climate wilderness, but when we apply it to science, moral judgement and other important things, we find that it is prone to all sorts of cognitive biases and logical errors.
So, to know what we know, we need to really carefully examine the evidence and the biases involved in its gathering and interpretation. Asking himself “what do I really know” Descartes arrived to the conclusion that “I think, therefore I am” is just about the only thing that can reliably be known and proceeded to develop his theory based on that.
