Descartes presented the main problem of philosophical idealism which was an awareness of the difference between the world as a mental picture and that of a system of external objects. Locke’s theory, on the other hand, encompasses the mind as the origin for modern conceptions of identity and “the self”. Locke was the first philosopher to define the self through a continuation of “consciousness.” He also speculated that the mind was a “blank slate” or “tabula rasa”. These two strategies are very different from the above strategies of Kant.At the beginning of early modern philosophy, in Descartes, we seem to see our familiar world slipping away. At the culmination of early modern philosophy, in Kant, however, we get our familiar world back through at a price. In the following essay I will discuss this process, beginning with Descartes, ending with Kant, and discussing two of the four philosophers we have examined this semester.In Meditation One Descartes gives three separate arguments. From these particular arguments one can conclude that we cannot claim to know with certainty anything about the world around us. Everything might seem probable but in reality that does not mean that it lacks doubt. If we can never be certain how can we know anything. This is the main reason for Descartes bring this issue up.Basically his entire argument is based on Scepticism. Scepticism is very important and is seen as an attempt for our knowledge and understanding of the world. It is really hard to doubt that someone really exists but there is no way that one could get rid of the idea of scepticism The one thing that we know is that Descartes does not just randomly doubt everything. He provides very concrete reasons for the things that he doubts. As he sets up this doubt he has to be very rational about it. If he does not then his argument is not going to work.