in our last session I outlined the four generic possibilities to explain reality as we encountered borrowing a bit from the ancient approach of Saint Augustine to this question I'm going to repeat those four principles and look at each one in Greater detail I said if something exists this piece of chalk or whatever it is that we can have four possible explanations for it the first is that it is an illusion the second one is that it is self-created the third is that it is self-existent and the fourth is that it is created by something ultimately that is self-existent and those were the four possibilities now it may seem to many people to be Herculean waste of time to really spend any time at all eliminating the first alternative that everything that we think exists is but an illusion but there have been serious philosophers in history who have argued precisely that point that the world and everything in it is simply somebody else's dream or is uh basically illusory and doesn't exist at all and so in order to deal with this first principle I'm going to call as my primary Witness Renee Descartes the father of modern rationalism the 17th century thinker who was also a mathematician who was very much concerned in his day about a new form of skepticism that had arrived on the scene of Western Europe following the 16th century Protestant Reformation because in the wake of the Protestant Reformation there was a crisis in authority previous to the Reformation Christians for example in the monolithic Church scene of Rome if they had disputes could appeal to the church to render a verdict and when the church gave the verdict that settled the controversy because the authority of the church was deemed to be at least sacrosanct and at best infallible and with the challenge to the authority of the church that came with the Protestant Reformation then the whole question of how can we know anything for sure became a serious problem for people and not only did you see the breakdown of church Authority but you also saw the breakdown and collapse of scientific Authority because in addition to the Reformation that occurred in the 16th century also in the 16th century the copernican revolution in astronomy took place which created the enormous crisis of the tradition of scientific Authority that had followed in the wake of of the ancient ptolemaic system of the universe and Copernicus upset that apple cart and raised all kinds of questions about the trustworthiness of science the controversy over the copernican revolution carried over into the 17th century where the Galileo episode became prominent in the life of the church where Galileo with the use of his telescope was confirming the mathematical theories of the 16th century astronomers by pointing his telescope into the heavens and demonstrating the verification of these theories of the 16th century so not only in Theology and philosophy but also in science there was a crisis of authority and what Descartes was trying to do in his philosophical inquiry was to re-establish some Foundation for certainty with respect to truth and he was looking for what he called clear and distinct ideas ideas that were indubitable ideas that could not be rejected without rejecting reason at the same time which ideas could then form a foundation for the Reconstruction of knowledge rather in the scientific sphere or in the theological philosophical Arena and so the process that Descartes followed in order to achieve certainty was to follow a plan of uncertainty or of skepticism what he did was he embarked upon a rigorous pursuit of skepticism in which he sought to bring doubt upon everything he could conceivably doubt in other words he wanted to give the Second Glance to every assumed truth that people held and he asked questions the epistemological question do we really know that this is true sometimes I I like to to go back to First principles myself and in fact my whole bent in philosophical inquiry is to keep coming back to foundational principles to the fundamental truths and I'll often make a list and I'll say to myself what are 10 things that I know for sure and I'll write them down and then I'll subject those 10 things to the most rigorous criticism I can to make sure that I'm not just believing them because somebody I liked taught them to me or because of my love lines my traditions the subculture in which I come from I want to know how do I know that these things that I think are true really are true and that principle is one of the most important principles for breakthroughs in any kind of knowledge one of the great principles for new discoveries is the principle of challenging assumptions because that's how philosophers break through musicians break through that's how scientists break through where they challenge assumptions that previous generations have been made and accepted uncritically and passed on from generation to generation that's how the ptolemaic system survived for over a thousand years is by people accepting theories without the theories ever having been proved and so we need to do that ourselves subject our own thinking to a rigorous cross-examination because you've all seen what happens in Trials where you hear somebody give their case and you hear one side of it and it makes sense and you're sitting there nodding yes yes yes until the cross-examination comes and people begin to raise questions about the testimony that you've heard and by the time you're done listening to both sides you're not sure who's telling the truth and so there's something valuable in that that doesn't mean you have to surrender to skepticism but this is what Descartes was doing he says I'm going to doubt everything I can conceivably doubt I'm going to doubt what I see with my eyes and what I hear with my ears because I understand that my senses can be deceived and we've talked about that going back to Augustine's bent ore you know that you look in the water and the ore looks like it's bent and and this is what Descartes did and he said not only that maybe this world is controlled by the Great Deceiver a great satanic demonic being who is a liar who constantly gives me a false view of reality and that maybe he is the master of Illusion and so he keeps bringing these Illusions in front of me to deceive me how can I know that reality is as I perceive it to be remember back to the basic foundational principles we started with one of which was the basic reliability of sense perception because if we cannot trust our senses in the basic rudimentary forms then we have no way of getting outside the interior of our minds and making contact with an external world and then and this is what is known as the subject object problem how do I know that the objective world out there is as I perceive it from within my own subjective perspective and as I say Descartes was acutely conscious of that so he he came up with some of the most Preposterous possibilities and he said no maybe if this doesn't make a lot of sense to think of a Great Deceiver uh producing this vast illusion out there but it's possible and he said and so if there if it's possible then I can't know for sure then reality that reality is as I perceive it to be so again what can I know for sure well after he went through this elaborate doubting process he came 2 his famous motto or slogan for which he is so well known the cogito ergo soon I think therefore I am he said no matter how skeptical I become the one thing that I cannot doubt whenever I'm doubting what it is that I'm doubting is that I'm doubting because if I doubt that I'm doubting it's necessary for me to doubt that I'm doubting so that if I doubt that I'm doubting I have to doubt to doubt that I'm doubting so there's no way I can escape the reality of doubt oh you say well I doubt it well if you say I doubt it you have proven the very point in dispute he says the one thing about which there's no doubt is that I'm doubting because if you doubt that you prove my premise and so he came to the conclusion that there's no doubt that I'm doubting and then he raised this question what is required for there to be doubt well he said for there to be doubt doubt requires cognition doubt requires thought conscious thought because doubt is an action of thinking without thinking there can be no doubting so if I'm doubting I know what that I'm thinking now at least I think that I'm thinking and you say you don't think that I'm thinking well in order for you to say you don't think that I'm thinking you must be thinking so I can't escape the reality that I am thinking because the doubt is to think and then he goes to the next premise that just as doubt requires a doubter just as thought requires a thinker so if I'm doubting I must conclude rationally that I'm thinking and if I'm thinking I must be I must exist because that which does not exist cannot think that which cannot think cannot doubt and since there's no doubt that I'm doubting it would mean also that I'm thinking and if I'm thinking I am also existing and so I come to the conclusion he says cogito I'm thinking Ergo therefore some I am now people who are not students of philosophy look at that elaborate process the Descartes goes through and say this is why philosophy is so foolish that somebody would spend all this time and all this effort to learn what everybody already knows who's alive and awake and conscious that they are in fact existing that nobody really is denying their own existence they're not really believing that they are simply a star appearing in somebody else's dream but again remember what Descartes was about he was a mathematician and he was looking for certainty at the philosophical Realm that would equal in force and Power and rational compulsion the certainty that can be arrived at in mathematics and so he goes through this process and he wants to get a primary principle he says that I can then crawl into my Dutch oven and then use the art of deduction where I'm not dependent upon my senses to come to an understanding of Truth and so I begin with a knowledge of my own self-consciousness now I said yesterday or the two lectures ago when we talked about presuppositional apologetics that for classical apologetics the starting point is not God Consciousness because we say only God can start there but the epistemological starting point of Christian apologetics has to be self-consciousness where you start in your own mind because that's the only mind you have at your disposal and that all thought begins with an awareness of a conscious awareness of one's think thinking or one's existence so that uh what Descartes is getting at here is whatever else may be in doubt the fact that I am a self-conscious existing person is not in doubt and that I do not have to look at my feet to know that I exist I am not dependent on any external perception I am now learning this just simply from the interior processes of thought in the mind I'm not dependent on external data so he stays within the realm of rational deduction for his conclusion now the reason this is important is that Descartes is this is disposing with the first option that reality is an illusion there may indeed be Illusions in reality but if we say that all reality is an illusion that would mean that nothing exists including myself and I can never even doubt the existence of myself without proving the reality of myself that's the point he's trying to get at that that first of the four Alternatives as a sufficient reason to account for the for the universe has to be discarded because his argument proves that something exists and that's something that exists if nothing else is his own Consciousness in other words to put it another way is that if I think that this piece of chalk is an illusion and it may be I said not if I didn't say that this piece of chalk proves the existence of God what I'm saying is that if this piece of chalk actually exists then it would prove the existence of God but this piece of chalk might be an illusion and so I have to take a little different path there and say if anything exists then God must exist that way I'm not hide bound to this particular bit of reality the piece of chalk because maybe this piece of chalk is an illusion I don't think it is but it could be theoretically but what I have to establish if my system is going to work is that something exists and there I think uh Descartes for solving that problem for me by proving the existence of himself now what are the things that he's assuming in order to arrive at his conclusion is it I mean there are philosophers who don't agree with this premise cogito aragosum who still insists that the there's no basis in reality for his coming to that conclusion and they point out correctly at least this far that there are certain assumptions that Descartes is making along the way in order to come to this conclusion and there are two major assumptions that he's making in order to come to the conclusion that because he's doubting he must be thinking and because he's thinking he must be existing the first assumption that he is making clearly is the epistemological principle of the law of non-contradiction he's assuming logic he is assuming rationality isn't he because he sang if I am doubt if there's doubt there if I am doubting if I doubt that I'm doubting then I must be doubting that is a logical conclusion based upon the law of non-contradiction where the existential irrationalists may say well so what that it's irrational he can still be living in an illusion where doubters can doubt without doubting and that's what irrational people say but remember that classical apologetics is only trying to show that reason requires the existence of a self-existent Eternal being if somebody is an atheist and said I don't believe in the existence of God because I don't believe in rationality I give them the microphone and say please tell the whole world that your alternative to theism is absurd save me the problem and the difficulty of having to demonstrate it I don't have to demonstrate it if you acknowledge it but I mean they have taken themselves out of any intelligent discussion as soon as they admit that their premise is one of irrationality what Descartes is trying to say is just as mathematics is rational just as sound science is rational so sound philosophy must also be rational and if you are going to be rational and if you are going to be logical you cannot deny that to doubt you must doubt and then the second premise that he is assuming is the second law that we talked about at the beginning of this course which is the law of causality when he says that doubting requires a doubter he is saying that doubt is an effect that requires an antecedent cause so some of the critics of Descartes would say oh well this doesn't prove that he exists because he's assuming logic and he's assuming causality and we don't accept those premises we say okay that's fine if you want to be irrational because remember we saw that the law of causality is simply an extension of the law of non-contradiction that the law of causality that says that every effect must have an antecedent cause is a formal truth it's it's as formally true as two and two is four because it's true by definition so if we assume remember I said it again you dare not negotiate the law of not contradiction and you dare not negotiate the law of causality because if you do you'll end up in absurdity but if you use these principles that are necessary for all intelligible discourse in all science in all philosophy in all theology then you cannot Escape I don't think the conclusion that Descartes gives that we can through a resistance logic through formal reasoning Alone come to the conclusion of our own existence which then satisfies that first premise about illusion and we can eliminate that as one of the possible alternatives for sufficient reason for the existence of the world