I think, therefore, I am. Descartes was not doing all of this simply to prove to the world that Rene Descartes existed. What he was searching for was a starting point for the pathway to certainty, to the pathway to a truth that really matters for everybody. He was looking for a rational, intellectual foundation for affirming not the existence of Descartes, but the existence of God. Even if you haven't taken a course in philosophy, most people have heard Rene Descartes' famous assertion, I think, therefore, I am. Although we may have heard it, that doesn't mean that we necessarily understand what he meant and what factors led him to that conclusion.
And that's what R.C. Sproul will consider on this Thursday edition of Renewing Your Mind. God made us in His image, and He created us with minds that can think and senses that can perceive. But how trustworthy are our senses when it comes to discovering truth? Although we generally assume their reliability, this is a question that has been wrestled with by philosophers, and it's helpful to consider the relationship between our minds and our senses. Before we get to today's message, I would like to invite you to join us next April in Orlando for Ligonier Ministries 2025 National Conference on the theme, I Will Build My Church.
And when you visit ligonier.org slash 2025 today, you can secure the early bird rate for you and your family. Well, here's Dr. Sproul on the mind and the senses. We continue now with our brief study of the Christian and the mind. We've been looking at some of the foundational issues of knowledge that became almost the preoccupation of Christian thinkers and philosophers in the 17th century. And we've been looking specifically at the work of the French Jesuit mathematician René Descartes.
And you recall that we made mention of his famous little slogan, Calguito Ergo Sum, I think therefore I am. And in our last session, I tried to give some background introduction for why a man of the intellectual magnitude of Descartes would spend so much time trying to prove his own existence. And we saw that in the light of the problems of the breakdown of authority, particularly in the church in the 16th century, that the question in the 17th century was, how can I know if anything is true?
How can I trust whatever knowledge I have received from my teachers, from the experts in various fields? And as I said, this became a time where careful scrutiny was given to the science of epistemology, which studies the question, how can I know anything? Now, Descartes, in light of the problem of skepticism that was confronting the church and the culture of his day, began his intellectual pilgrimage by declaring war on gratuitous assumptions. He said, I am going to doubt everything that I have ever learned. I am going to doubt everything that I can conceivably doubt.
I'm not going to take anything for granted. Now, I think we will see, I hope we will see that there still were a few things he took for granted that he didn't totally abandon, but the process was one of rigorous and systematic doubting. He looked at things like this. He said, how can I know for sure regarding anything that I observe with my eyes or hear with my ears or taste with my mouth? In other words, how can I be certain of anything that I perceive with my senses? Now, you know, in our day and age, there is a predilection in our culture to say unless we perceive it with the senses, we can have no confidence in its truthfulness at all. We say, I want to see it, taste it, touch it, smell it, or so on.
We want physical, tangible, sensible evidence to believe whatever it is that we believe. But what Descartes said was, I'm going to challenge my very ability to perceive, and he basically challenged this on two separate levels or planes. On the one hand, Descartes focused in on what we call the subject-object problem. You as a living, breathing, thinking person are subject, and everything that exists outside of you could be called objects.
You're looking at me. I'm an object of your knowledge, even though in myself I am a subject. As I look at you, you're an object of my perception. This piece of chalk that I'm holding here is an object about which I'm now speaking. Now, the question in the old subject-object problem is this. How can I know for sure that the external world, the objective world, the world that exists outside of my own mind really exists as I perceive it?
Now, this is no small question. We're asking the question, how accurate is my perception of reality? Is everything the way it seems to be as I perceive it? Or is there some kind of built-in distortion that takes place in this transition between the external world and my mind? My ideas are in my mind, and my ideas about you are not gained by having a direct link-up between my mind and your mind.
The only way I can get into your mind is if you choose to tell me something or reveal something about what's in your mind, and you do that in various ways. You may act it out. You may speak it.
You may write it. But for me to get in touch with that, I have to use one or more of my five senses. I'd have to read with my eyes or hear with my ears, do you see? Or if I were blind, I could read it with my fingers, with Braille, but some part of my body would have to be engaged in this communication process between us. You see, the body is your personal transition to the world around you.
Your way of getting from your mind to the external world is your body. Now that's something that was understood clearly by the writers of the sacred Scriptures. You hear Peter, for example, saying, we do not declare unto you cunningly devised myths or fables. That is, we're not writing fiction, stuff that we've made up out of our own speculative imagination.
But what did he say? But we declare to you that which we have seen with our eyes and have heard with our ears. Well, we think of doubting Thomas after the resurrection, saying unless I can put my hand into the wounds on his body, I will not believe. In a word, what Thomas was asking for was what we call today empirical verification, that is proof or evidence that is founded on sense perception, on seeing, tasting, touching, hearing, and so on, so that the mind, according to this theory, should not adopt or embrace as true that which cannot be verified or proven by the five senses. Now it's precisely at this point that Descartes sort of turns the tables because of this problem of the subject and the object. What Descartes is really saying here, ladies and gentlemen, is that rather than sense perception being the highest form of proof and the preferred method of arriving at certainty, he was saying that it is an inferior way of getting at truth and a very dangerous basket if you put all your eggs in it.
He was not decrying or denying the utility of sensation, but he was trying to show the limits of learning truth simply through what you see, taste, hear, touch, and so on. Because, again of this problem, how do you know that when you are seeing something, your eyes aren't playing tricks on you? You know what a mirage is, where you think you see a pond of water, but there's no pond of water there. What is a hallucination? Hallucination we tend to understand as a distorted picture of reality. I mentioned this before that one of the fascinating debates earlier on in this century took place at Harvard when the crown prince or the high priest of the new drug movement, particularly LSD, Timothy Leary, was performing experiments in the psychology department with the use of so-called hallucinogenic drugs like piote and others. And it was found out that he was introducing a chemical substance called LSD into these experiments, and he got into big trouble. And so there was a court trial about this case because it was against the law to be practicing this trade with the use of hallucinogenic drugs. And a hallucinogen is something that distorts the mind's perception of reality. So they hauled Timothy Leary into court in Boston, and for his defense he more or less invented or at least popularized a word that became overnight an integral part of the pop vocabulary of America. It was the word psychedelic.
Remember that? The defense Leary put on was this. He said that under the influence of this drug, mind-altering, chemically-altering drug, LSD, that what happens is not that the mind's apprehension of reality is distorted, as is in the case of a hallucinogenic drug, but rather the mind is now enhanced. In other words, in simple terms what he was saying is LSD gives you a more accurate picture of what's actually out there than you have without the benefit of LSD. And he had artists and musicians and people creating to the witness stand and artists saying, wow, when I was tripping out on LSD, I was seeing blends and harmonies and hues and tints of color that I had never been able to perceive with such acuity as I did when I was under this drug. Or musicians saying, wow, my sense of harmony was raised to a whole new dimension when I was under LSD. But what we're interested here from an epistemological perspective is this. Who can prove Leary wrong? How do you know that reality is as you perceive it?
We do know, for example, that there are built-in limits to our sense perception. I tell the story of when I was a little boy and my dad got me a dog, and my mother sent me to the hardware store to buy a doggy whistle. And I paid for this doggy whistle. I took it home, and I blew it. It didn't work. So I went back to the store, and I told this owner, I said, I bought this doggy whistle.
It doesn't work. He said, what do you mean it doesn't work? I said, well, listen. I blow into it, and I think he said, wait a minute.
He said, don't you understand that this dog whistle makes a sound at such a high frequency that your ear doesn't hear it, but your dog will hear it. Go home and blow it a few times. See what your dog does.
So I went home and blew it a few times. Sure enough, here comes the dog. So that was my first little scientific experiment with understanding that some animals have far more developed and more acute senses of what's going on around them than we do. We know that there are animals who have a far more advanced olfactory sense than we do. That is, they can detect, they can track just on the basis of smell things that are miles away. We know the radar units of the bat and so on.
We're all familiar with that. So why do we make the assumption that reality really exists as we perceive it? You know, this is what provoked the question in the 18th century if a tree falls in the forest and there's no one there to hear it, was there any sound?
And Bishop Barclay's essay at Perkipi that to be is to be perceived was an advance in this issue, and it's what provoked the 20th century question, as I've mentioned before. If a man speaks in the woods and there's no woman there to hear him, is he still wrong? But in any case, you get the idea here that if I look at the audience that is in front of me today, and I'm trying to figure out how tall a man is who's sitting in the back row who's a retired Chicago policeman, and he's sitting there, and I just look at him and eyeball him, and if I try to use my thumb as a gauge, if I hold my arm out in front of me and close one eye and hold my thumb over this man's body, I can cover his entire body with the thumbnail of my right hand. So I say, okay, I know what I'll call that policeman, palm, thumb, because he's no bigger than my thumb.
Now, what's wrong with this equation here? It's from this distance that I am removed from him, and if I put a small object in front of my eye, that small object will obscure my entire sight of that man, and it would be a ludicrous inference to conclude that he's no bigger than the nail on my thumb. But you see, we have learned through the experience of daily life to make those adjustments of depth perception and the like. But Descartes says, how do you know that this isn't all one big distortion? How do you know that the lunatic in the insane asylum isn't having the accurate perception, and we're the ones that aren't perceiving reality truthfully?
Or he says, suppose somebody else gets into the mix. One thing that Protestantism and Roman Catholicism both believed in was the devil. And he said, how do you know that what you think you are seeing or think you are hearing isn't a trick conjured up by the devil? And he would point to such things as the appearance of the witch of Endor in the Old Testament who conjured up Samuel for Saul, and was that a fake? Or did the devil really have the ability to produce Samuel, or was it an illusion?
How do you know? And so he considered the possibility of Satan as being the great deceiver who went about causing people to come to a distorted knowledge of the truth. And so what I'm saying is that he went through this rigorous process doubting everything that he could possibly doubt.
Authorities disagree, so he can't appeal to authorities. How can he know anything for certain? Well, he boiled it down to this. He said, well, there's one thing I cannot doubt without affirming at the same time that I am doubting, and that is I cannot doubt that I am doubting, because in order to doubt that I am doubting requires that I do what? That I doubt that I'm doubting. So that if I doubt that I'm doubting, I most certainly am doubting. And if I doubt it, I'm proving it.
Do you see that? And he said, okay, so one thing I know for sure is that I'm doubting. But if I know that for sure, I know something else, that in order to doubt, doubt itself is some kind of thinking.
It requires consciousness. It's not just a tingle in my toe, but it is a negative affirmation or denial in my head, in my thinking. So if I'm doubting, I must be thinking. Well, maybe I can doubt that I'm thinking, but in order to doubt that I'm thinking, I think, I must think that I'm not thinking. So even if I think that I'm not thinking, what am I doing? I'm thinking. So no matter how I come at this, I can't escape the indubitable truth that I'm thinking.
And thought must have a thinker. And so he says, if I'm doubting, I'm thinking. If I'm thinking, I'm being. If I'm thinking, I am. Now I know that I'm thinking.
Cogito, I think. Therefore, I am. But again, ladies and gentlemen, understand this as we'll look at more in the next time. Descartes was not doing all of this simply to prove to the world that René Descartes existed. What he was searching for was a starting point for the pathway to certainty, to the pathway to a truth that really matters for everybody. He was looking for a rational intellectual foundation for affirming not the existence of Descartes, but the existence of God.
Again, why would we go through so many intellectual gymnastics to come to something, a conclusion that most of us just take uncritically and automatically as a given of our experience? Even the great Emmanuel Kahn did not try to prove the existence of the self. He said that this is the transcendental apperception of the ego. You can't perceive yourself as a self. You can't see yourself, your innermost self, or taste, but you cannot deny it. It's so integral to your own consciousness. And so what we're saying here, as Descartes was trying to indicate, is that all thinking begins with consciousness.
And so from the Christian perspective, we have to ask, how does our consciousness include and relate not only the consciousness we have of ourselves, but how does the consciousness of our self relate to our consciousness of God? You're listening to Renewing Your Mind, and that was R.C. Sproul from his 12-message series Think Like a Christian.
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Simply search for Ultimately with R.C. Sproul wherever you listen to podcasts. Tomorrow is the last day that you'll hear a message from Think Like a Christian, so be sure to request lifetime digital access to all 12 messages when you give a donation of any amount at renewingyourmind.org or when you call us at 800 435 4343. We'll also send you Dr. Sproul's book, The Consequences of Ideas, which is his overview of philosophy, so request both resources today at renewingyourmind.org or by clicking the link in the podcast show notes, but be quick as this offer ends tomorrow. What is the scientific method, and is it compatible with what the Bible teaches? Tomorrow R.C. Sproul will consider two ways of knowing, here on Renewing Your Mind.
