According to indirect realism, we acquire knowledge of external objects by virtue of perceiving something else, namely appearances or sense-data. What is it that makes that attitude reasonable? The computer produces what seem to be genuine sense experiences, and also responds to your brain's output to make it seem that you are able to move about in your environment as you did when your brain was still in your body.
Thus, according to Williamson, justification, truth, and belief are necessary but not sufficient for knowledge. But the second occurrence of "identical" refers to numerical identity. Think of it like the mortar between bricks that begins at the very bottom level, locks them solid, and moves upwards to lock the higher bricks into place.
But just as there are no signs that will allow us to distinguish between waking and dreaming, there are no signs that will allow us to distinguish between beliefs that are accurate and beliefs which are the result of the machinations of an evil demon.
These particulars are given to us through sense perceptions. Also, what is the principle that human knowledge reaches in explanation, and is considered a general primary criterion for distinguishing truth from other things?
Reliabilism says that the justification of one's beliefs is a function of, not one's evidence, but the reliability of one's belief sources such as memorial, perceptual and introspective states and processes. Let us see why.
This is also where we find the Truetemp example.