Philosophy 101: Skeptical Hypothesis
As noted, skepticism (in philosophy) is the position and belief regarding a general doubt surrounding human ability to possess knowledge, or about knowledge in general. One of the most famous arguments for a broad form of skepticism (as opposed to more specific types such as moral skepticism) is known as a skeptical hypothesis. The earliest argument from a skeptical hypothesis comes from Renee Descartes, who discussed the possibility of an evil demon who through his machinations of deceit and cleverness was able to actively control and manipulate our every experience. This would mean that our own perceptions and experiences were in fact false, and raised peculiar doubts about the validity and truth about our own ability to have knowledge of anything.
Another form of this argument is known as a "brain in the vat," which is similar to Descartes original argument but instead of active deception also incorporates elements of another problem that arises. In another argument, Descartes raises the impossibility of determining whether one was awake or dreaming; absent the possibility of active deception, this matter still concerns the possibility of the inadequacy of our perception in determining or ascertaining true knowledge. The "brain in the vat" argument poses a philosophical doubt upon knowledge, truth, reality, and the mind itself. Often times this concept has been used in many movies and science-fiction novels where the human brain is removed from the confines of the skull and supported inside a vat or synthetic laboratory setting where it remains fully functional and perceiving experiences, albeit these experiences would be false (since the brain is confined not within a skull but rather a piece of laboratory equipment). Despite the scientific questions regarding the reality or possibility of taking the brain out of the human skull and placing it in a vat where it is hooked up electronically to a computer which sends electrical impulses to the neurons to give the brain the same type of responses it would otherwise receive, the point is to demonstrate fallibility of our having full knowledge (or any type of knowledge) regarding our experiences and places a significant amount of doubt on the otherwise accepted concept of general truth.
The simplest and most basic format of the argument makes the claim for a type of global skepticism regarding knowledge/truth in general. First, imagine a brain in a vat of liquid hooked up to a super-computer which is capable of generating the exact same impulses as it would otherwise receive and this serves as its only means of generating any experience with the outside world. The brain itself relies only on these electrical impulses which can be wholly controlled by the operator of the super-computer. If the operator wished to do so, it could send impulses to the brain in the vat that told it that it was walking down the street eating an ice-cream cone. Imagine the brain then believing this to be the case just as if it were happening to you or me. We could taste the ice-cream, feel the pumping of our legs as we walk down the sidewalk, feel the heat of the sun on our skin, and visualize the entire experience. However, since the brain in the vat is receiving the exact same impulses as if it were really a normal brain inside a skull, and completely unaware of its true environment, it would never know the difference and thus every experience we have as human beings would be indecipherable from a brain in our skull or a brain in a vat. Since we can never know, we cannot place any certainty on the possibility of truth or validity of any belief, experience, or perception, and thus we can only conclude that every one of these might in fact be false. Note, this is not a definite claim to the falsehood of every experience - since that would not be a skeptical claim; rather, it is raising doubts about our beliefs in the truth or validity of our experiences in general.
Another example of this type of argument can be said about a virtual reality world. What if we were not sitting in our living rooms, watching television, with our family. Instead, we were plugged into a machine in a secret laboratory where all these visual, auditory, and other sensory impressions were generated by a computer in an entirely virtual reality manufactured by someone (or something) else. If our only experience is that which the computer is generating for us and we have no idea as to what's really going on, then we could not possibly tell whether or not everything is really real or generated by a computer. Such scenarios and hypothetical situations seem beyond believable, but outside the context of the science-fiction world - it raises a certain doubt about how we are able to tell what is real, or what is true. None of us can say with any valid certainty that we're NOT a brain in a vat, or hooked up to a virtual reality simulator - even though everything seems so real around us.
The real point behind this, and other skeptical hypothesis arguments, is to demonstrate the fallibility of our sensory perception is when determining reality or truth. The possibility that experiences could be actively created by someone or something else may be the content of science-fiction, but it says more about our perceptive abilities as human beings and our tendency to take perception as definitive truth is a key part to our ability to function in an ever growing complicated environment of external stimuli. While this may not have much practical application for most people, it still remains a fundamental question (and problem) in modern philosophy.See more info about do my computer programming homework