Philosophy

Rene Descartes, often referred to as the Father of Modern Philosophy, was a rationalist who believed that human reason is the fundamental source of knowledge (Kisner 144).  Descartes applied the philosophical technique of methodological doubt in his Meditations on First Philosophy (Albl 20).  According to this method, one must doubt everything that can be doubted, and refuse to accept anything as having been known unless it is established with certainty.  However, there is no certainty in any matter available to human understanding or perception.  Descartes doubts the things he sees and experiences.  He even doubts his good old belief in Gods greatness.  It is eventually discovered that Descartes is concerned with a sense of having no knowledge whatsoever, given that his human understanding and perceptions have failed to meet the criteria of being certain or foolproof (Albl 20-21).  Still, almost everybody that has learned about Descartes can tell with certainty that the philosophers most famous statement is I think, therefore I am.  In other words, the philosopher is permitted by reason only to believe in his own thoughts  or doubts, as in the case of Descartes (Albl 21).  Nothing is known with certainty it is the mind that gathers knowledge, but even ones thoughts can be doubted because they may or may not produce correct answers or explanations as in two plus two is always four. 
     Descartes provides his explanation about the uncertain nature of human perceptions in the following example
I have formerly accepted as true and certain those things I learn through the senses.  Like the fact that I am seated by this fire, in a dressing gown, with this paper in my hands.  And how could I deny that this body is mine, unless I was as mad as those whose cerebella are so clouded by black bile that they believe they have an earthenware head or a glass body  Yet, I must remember that I have dreams, which are almost as insane.  Often I have dreamt that I was dressed and seated near this fire, whilst I was lying undressed in bed  It seems to me that I am now awake, but I remind myself that I have dreamt that too.  Yet even dreams are formed out of things real and true (Descartes) 
Descartes is describing the nature of dreams with reference to reality as ordinary people see it.  If I see myself writing this paper in a dream, and the dream seems truly real to me at the time I am dreaming in bed, I would remember the dream while writing this paper today.  This remembrance would lead me to wonder whether I am dreaming at this point, too.  Given that both the dream and the reality of writing this paper appear real to me, what was the purpose of my dream  And, what is truly real  Was my dream more or less real than the reality I am living just now  Seeing that I am doubting the reality of my dream versus the reality I am living right now, is reality not relative to the real which is meant to be solid and of an absolutely certain or explainable nature 
     Descartes provides another example to reveal the uncertain or relative nature of human knowing or perception
Let us consider one simple corporeal thing  this piece of wax freshly taken from the hive, with the sweetness of its honey and the aroma of flowers.  It has its color, its figure, its size.  It appears hard, cold, and if you strike it with the finger, it will emit a sound.  But while I speak, I take it near to the fire the smell, color, shape is all destroyed.  It becomes liquid, it heats so that scarcely can one handle it, and when one strikes it, no sound is made.  All sensation is changed, yet we confess that it is the same wax. (Descartes)
The fact that the wax changes its shape, form, and texture shows that it is not an unchanging object that one would recognize as a certainty.  The form of the wax is, in fact, relative to the conditions through which it passes.  Furthermore, Descartes reveals that human perceptions cannot be based on sight alone.  The wax changes its shape, form, and texture.  Therefore, if we were to base our understanding or knowing on our sight alone, we would conclude that wax is a separate object in its solid form, and another one in liquid form.  Moreover, we cannot base our understanding on imagination alone, seeing that our imagination does not allow us to include an infinite number of possibilities in our understanding of the texture of the wax.  We are led to believe, as a result of this reasoning, that human perception of external objects, that is, the wax and the act of sitting by the fireplace, is entirely based on judgments of the mind and the conclusion it reaches (Sepper 168).  Then again, the mind could be confused enough to start doubting whether a dream is real, or whether that which it knows as reality is a dream.  In the end, I would only be able to reach the conclusion that I think, therefore I am.  It does not mean that I would trust all that I have thought, however.   
     Like the Father of Modern Philosophy, David Hume also believed that the sight alone cannot provide humans with real knowledge about external objects.  In his An Enquiry Concerning Human Understanding, the philosopher has written
Let an object be presented to a man of ever so strong natural reason if that object be entirely new to him, he will not be able, by the most accurate examination of its sensible qualities to discover any of its causes or effects.  Adam could not have inferred from the fluidity of water that it would suffocate him, nor from the warmth of fire that it would consume him. (Hume)
Neither reason, nor imagination could reveal to a man the meaning of an external object in his first experience with this object.  Unlike Descartes, Hume rejects the certainty of personal- or self-identity because he has no faith in the substance of the mind (Flage 69-71).  This is because the mind does not comprehend the reality of all things that the human being perceives as external objects.  Hume writes further
We fancy that from our first appearance in the world we could have inferred, without experience, that one billiard ball would communicate motion to another or that a stone raised in the air without support would fall.  If we could pronounce concerning such effects, without consulting past observation, after what manner, I beseech you, must the mind carry out this operation  Is there anything a priori which might prevent the stone from moving upwards or the or the billiard ball from remaining at rest  In all our reasonings the mind can never find the effect in the supposed cause. (Hume)  
In Humes view, one may only express skepticism with regards to things that he or she has not yet seen or understood.  The philosophers comprehension of knowing or perception neither denies nor affirms the existence of external objects.  Hume believes that individuals may only know about the external world through their perceptions of it.  And, these perceptions may be accurate or inaccurate, as in the case of the mirage which looks real but is not (Flage 172).
     Humes philosophy leads us to doubt our perceptions while doubting them not.  Based on his worldview, science can make great progress with the understanding that our perceptions and knowledge are incomplete, and therefore, we may continue to move forward in search of new insights that may possibly clarify our perceptions and understanding of external objects.  Although much of Humes philosophy may remind the reader of Descartes view of the world, the reader is led to doubt his or her personal identity as Hume does, given that the mind does not always lead the thinker to the right conclusions (Flage 130-133).  If I were the first person on earth to throw an object in the air, I might have thought that that object would continue its upward movement instead of being pulled down by the force of gravity.  Hence, I would have made a wrong conclusion about the object of my perception.  I thought, therefore I was.  All the same, I did not want to be led to a wrong conclusion by my mind.  Why did my mind mislead me into thinking that the object thrown up in the air would continue its upward movement  Seeing as I did not, even for a moment, wish to be misled by my mind, and did not desire to be untruthful to myself, my sense of I am is a falsehood given that this I am is in my mind, and my mind can lead me to wrong conclusions.  I can make mistakes, and therefore, the substance of my mind is not truly real either  Just as the mirage, which is there and not there at the same time, my mind is with me today a perception the knowledge of which may be furthered through greater understanding with the mind alone.  Hence, my mind or I learned with the help of my sight that an object thrown in the air must fall. 
     According to Descartes definition of what is real, the substance that the mind is made of cannot be understood with certainty either.  What is more, one must agree with Hume that reason would not always lead people to right answers for all questions.  This is proved by my mistake in judging that the object thrown in the air would continue its movement upward.  There was every reason for me to believe that the object would continue moving upward.  Yet there was no reason for me to believe that.  Given the uncertain nature of the use of reason, too, one must conclude that human reason may not always provide us with correct explanations.  Hence, everything is open to doubt.