Any truth that can exist in one can exist in the other. For this reason, there is no precise way to know whether an experience was dreamed or not. The arguments against this are purely speculative, based on personal experiences, and perhaps those of others, but that is not enough. Just because one person does not feel pain during a dream, signifying some sort of differentiation between the two states, does not mean that another person does not feel pain. Because all evidence against this argument is purely speculative and circumstantial, this proves that we cannot prove consciousness at any given time with Cartesian certainty. A waking state exists, however, our ability to differentiate it from a sleeping state is impossible, leading to confusion about experiences. Having Cartesian certainty about whether or not we are dreaming at any given moment allows us to evaluate any other aspects that might skew our findings. Because we can sleep at any time, who's to say that our knowledge and experiences aren't all dreamed? The brain, although a complex mechanism, is not complex in coming up with the ideas that we have experienced within it. We can form new ideas based on our experiences, but the basis of these must have been experienced at one time or another. Our brains need credentials for knowledge, and in order for us to know absolute truths, we need to understand that some truths may not be as true.