How much do we know? Do we know anything at all? Or can we even know? More than four centuries ago Descartes meditated to these questions and had surprising insights and ideas. He reflected upon his life and found that much of his former opinions and beliefs appeared to be false after some time passed. Much of what he used to believe when he was young eventually turned wrong or delusive as he was aging. Descartes says that while his memories and knowledge are not certain and may appear false, how can he trust them. Moreover, how can he judge whether the present beliefs that he holds are truthful? Answering this question he explains, that things of empirical or physical nature are very uncertain. Our concepts of the universe, of how human body works or on how chemical reactions pass, were numerously debated and altered over the course of history. The things originating in purely mind activity are more reliable. For example, two and two will always be four. Nevertheless, the question much more laborious and troublesome Descartes presents. Our knowledge and beliefs are based on the information that we perceive from the external world. We employ our sensory system to interact with the world and to form knowledge itself. So, most of our knowledge is sensory-based. The senses, however, are easily tricked and deceived. Descartes states that when we sleep and see dreams, we do not perceive real world as in our mind we may be wandering in the fields and forests while in reality we rest and lie in bed. Following this sleep explanation, he says that if our senses are fooled this easily then how can we be sure in the knowledge we possess. Descartes assumes that an evil and omnipotent demon might deceive all of his senses. If this is the case, then he cannot be sure about whether he really has arms, legs, and body at all. He also finds that in such case he cannot trust his feelings of reality and his previous experience since all of that can be nothing but an illusion. While all of his senses are tricked, there is no way for him to find what is real and what is not (Descartes 8). In this situation, any knowledge is meaningless because it does not pertain to the real world. The most important, however, is that we cannot tell whether we are not tricked by an evil demon now. And if we are then all our knowledge is meaningless.
If such device is invented and its interface directly connects to brain to produce the sensation, it still will not resolve the problem of sensory-based knowledge. The question is how this device makes the comparison. To judge the adequacy of the perceived data, this module should evaluate the perceptions comparing them to something else. This something is evidently the device’s perception of reality. For example, it may have cameras or other sensors, or it can be calibrated to compare the neuro-signals to their reference values which were measured when a human perceived pure and unaltered reality. Having this device will allow us to judge if we are hallucinating or dreaming using one of the abovementioned mechanisms. But this judgement will be based on the comparison to the reality we previously perceived or to the reality that the device itself perceives. Both of these realities, however, reside inside our reality. So both of these judgements base on the fact that the world we perceive or the world where this device is produced is real. However, this may be not the case.
In or dreams, we can perform all kinds of actions – we can run or swim extremely fast, we can jump for 20 meters or even fly, but we also can invent all sorts of things and devices. Such device can be invented inside someone's dream and perfectly distinguish reality from hallucinations. But what it will perceive as reality, will, in fact, be only a dream. And after waking up, all of that will be gone. The accuracy bar depicting the percentage of reality in our perception will stimulate our brain directly but what if the brain itself does not exist. This mention is very critical to this whole issue. If we are inside an illusion, and we never have been outside this illusion, then all we make will also pertain to the illusion. We cannot create something that is outside our understanding of the world. As Descartes asserted, the painters often create the images of fantastic creatures, but all those creatures are only a blend of existing humans and animals (Descartes 7). The opposite side of the argument is also true. Everything invented in certain reality, or a system of perceived knowledge will only work inside this reality. So, even if such device will be produced it will not be able to penetrate the boundaries of the reality where it was invented. Even the most sophisticated inventions made in our dreams cannot step outside our dreams and assess reality. Concluding all said above we can see that such device assessing the reality of our senses will not distinguish our perceptions from illusion in evil demon scenario. The main reason is that it was constructed employing our senses and perception which may be initially false or delusive. So, this device will be useful for finding out whether or not you are hallucinating or sleeping but it will not be able to counter radical skepticism and resolve the problem of knowledge.
Descartes, Rene. Meditations On First Philosophy. Internet Encyclopedia of Philosophy, 1996. Web.