Consider the veridical experiences involved in cases of perception; cases where one genuinely sees or otherwise perceives an object for what it is.
As in the case of Sense-certainty, here in the case of Perception, by following the protagonist consciousness's efforts to make this implicit criterion explicit, we see how the criterion generates contradictions that eventually undermine it as a criterion for certainty.
But a difference between them is that in the case of thought, how the object of thought is at the moment one is thinking of it does not in any way constrain one's thinking of it; but in the case of perception it does.
In the case of Perception, the emergent new shape of consciousness, the Understanding, explored in Chapter 3, is a shape identified with the type of scientific cognition that, rather than remaining on the level of the perceived object, posits underlying forces involved in the production of the perceptual episode.
It might be almost anything: in the case of "Perception," a motif that could have come from a lost Tchaikovsky violin concerto or a sudden intervention of recorded drubbing from strings played with the wood of the bow.
A sense-datum, he says, is supposed to be something of whose existence we know in every case of perception.
For any given thinker S and an arbitrary object of thought O: Unsurprisingly, the same questions which arose in the case of perception also arise here.
In the case of perception, or memory, it is clear that it is impossible to possess such a proof, so a more relaxed standard is required.
In the case of perception, the mind is directed to present material objects and properties; in the case of memory, the mind is directed towards past events to which the person was agent or witness.
In the case of perception, what makes it possible to seem to see or hear what is not there is that one's experience may in various ways be inaccurate, nonveridical, subject to illusion, or hallucinatory.
