Abstract

In the modern philosophy the theory of knowledge has been among the main issues of philosophical researches, made by philosophers such as Descartes, Locke, Hume and Kant. That is why they have to be, primarily, regarded as the epistemologist. If we classify the theory of knowledge under three categories: the range of knowledge, the sources of knowledge, and the nature of knowledge, difference between epistemologists' ideas will become clearer. In particular, as regards the range of knowledge, there is a wide spectrum of various ideas, some of them opposing some other. At one end of this spectrum is skepticism claiming that our knowledge of the world is much less than what we usually think. Some extremist skeptics claim that our knowledge does not go beyond the sensible issues and the everyday experiences. At the other end of this spectrum are various kinds of realism, maintaining the possibility of man's knowledge of the internal and external world. Some other theories are centered in the spectrum. One of such theories is phenomenology.As regards the possible sources of knowledge also, the present philosophical ideas lead to a wide spectrum. At the one end, there are classical empiricists, such as Locke and Hume. At the other end we find Plato, who believes that the true knowledge cannot be found through experiment. In the middle of extremist rationality and extremist empiricism, there is a more moderate position, called classical rationality, which is supported by philosophers such as Descartes and Leibniz.The nature of knowledge, also among the main axes in epistemology, is, since the olden times down to the present time, disputed on. Particularly, in the recent times, this axis has attracted the attentions of philosophers and caused them to analyze the knowledge to find its main constituent.