Commentary on Descartes

Rene Descartes began his philosophy by assuming that everything could be an illusion. He was trying to overcome extreme skepticism by finding if anything existed of which one could be certain. By his famous dictum, "I think, therefore I am," he concluded that the one certainty he had was that he existed. 

Later, he speculated that the mind interacts with the world through the pineal gland. But he forgot that the pineal gland, being but an object to the mind, could itself be but an illusion. Had he thought of that, he would have realized that his thoughts must be solipsistic, and he would have been forced to return to his skeptical position that everything could be an illusion.

However, whether everything is an illusion or not, one can still be certain that an experience in process is happening. The quanta of experience is happening. Light and darkness, shapes and mist, hard and soft, motion and stillness are happening whether these are illusory or real. This can only mean that the basis of all experience must be consciousness. Consciousness itself must be real whether everything else is illusory or real. All of the objects of consciousness may be an illusion, but consciousness itself has to be real.

At this point, consciousness realizes that consciousness can be conscious of itself, and that this self-consciousness is located to one position. Since consciousness itself must be real, then so must self-consciousness. Self-consciousness localizes consciousness to one particular set of experiences. In this way, one can be certain that one's self exists.

Nevertheless, everything except consciousness could be an illusion. But since there exists no known way to determine whether everything except consciousness is real or an illusion, then by default it really does not matter. One might as well accept everything as real because no method exists to test whether everything is real or an illusion.