Sunday’s Sermon (recycled)

Cogito ergo sum

Thank you for inviting me to speak with you today. And thanks to the committee for responding positively to my requests.


  1. Bertrand Russell – “Do not feel absolutely certain about anything.” (and one wants to respond: “Are you certain about that, Lord Russell?”)
  2. Mario Livio – “While doubt often comes across as a sign of weakness, it is also an effective defence mechanism, and it’s an essential operating principle for science.”

I want to tell you a story. Last time I was here I told you about our first born son painting a picture of God. Now from our second born son: Many years ago and in another country as I was sitting in the living room after classes one day reading the newspaper, I heard a an argument on the front porch and after some harsh words a scream from our daughter. I went outside and she reported that her brother had pushed her off the porch. She was not hurt; just angry.

I looked at her tormenter with my harshest look and said to him, “If I were you I would NOT do that!” He apologized to his sister and they went on playing. I went back in to finish reading the paper.

After a few minutes he came in and looked at me, and when he had my attention he said, “But Daddy, you are wrong; if you were me then you would have done what I did.”


The law of identity!


I had to explain that we humans are not always to be taken literally and that what I had uttered was a threat.


In the academic setting the usual procedure is first to have the lecture and then to have the quiz. But I like to give the quiz first. I have some paper and pencils if you need some.


First the quiz:


There are four questions. You are not allowed to ask questions. No cheating! No talking to your friends for help. I will ask the questions and try to speak clearly and powerfully.


  1. Imagine the border between the USA and Canada. An airplane takes off from LA bound for Vancouver. It runs into a massive storm and is blown off course again and again. Eventually the plane runs out of fuel and crashes precisely on the border between the two countries. The question is: In which country do they bury the survivors?
  2. Print a small case i with a dot over it.
  3. Imagine a rail line running through a meadow. There is a baby bull eating grass on the line. Nearby is the mother bull. Further away is the papa bull. The train runs into the baby bull and changes it into hamburger. The question is which bull is closer to the cadaver of the baby bull?
  4. Imagine that you are a bus driver. In the morning you start out from the yard with an empty bus. At the first stop 6 people get on. At the second stop 4 get on and one gets off. At the next stop 5 get on. At the next stop 8 get on and 2 get off. At the next stop you have reach your turn around point. The question is: How old is the bus driver?


Discuss the quiz.



I call the talk In Praise of Doubt but I think “Praise the if__then__ construction” might be just as informative.

Adam Frank in a recent piece in the New York Times presents a strong case documenting the decline of science in North America. He writes, “Today, however, it is politically effective, and socially acceptable, to deny scientific fact.” Almost half of citizens in the USA believe in creationism. A large percentage is made up of climate change deniers. North Carolina, for example, has banned state planners from using climate data in their projections of future sea levels. That seems so nonsensical that it must be based on a confusion arising from the ambiguity in the term LAW. On the one hand law is a system of rules and guidelines which are enforced through social institutions to govern behavior. And on the other hand law as observed regularity. We cannot, for example, pass a law in the BC Legislature banning gravity in our province.

So many Oregon parents have refused vaccination that the state is revising its school entry policies. And all of this is happening in a culture that is less engaged with science and technology as intellectual pursuits than at any point I can remember. Everyone has her cell phone but fewer and fewer know how it works.

What do Plato’s cave, The Ring of Gyges, Bertrand Russell’s teapot, William James’s squirrel, John Searle’s Chinese Room, Descartes’ evil genius, Schrodinger’s cat, a brain in a vat, and Judith Jarvis Thomson’s unconscious violinist have in common?  And what do they teach us about critical thinking?

Ring of Gyges is a mythical magical artifact mentioned by the philosopher Plato in book 2 of his Republic (2.359a–2.360d). It granted its owner the power to become invisible at will. Through the story of the ring, Republic considers whether an intelligent person would be moral if he did not have to fear being caught and punished. Plato asks the general moral question: if you could do a bad thing and no one would know it was you, would you do it? Or, to put the question another way, are humans naturally good, or would we all do wrong if we could get away with it?

A more contemporary thought experiment in the area of moral philosophy comes from the philosopher Judith Jarvis Thomson who asks in a famous paper: does a person who is kidnapped by the “Save the violinist” musical appreciation group, and then connected to their famous violinist in order to save his life when his system fails have a moral obligation to stay connected? What if the famous violinist needs you for, say, nine months? Do you still have an obligation? Thomson is presenting a typical reductio ad absurdum argument in order to bring out certain weaknesses in the strongest argument used to prohibit abortion.

Russell: “If I were to suggest that between the Earth and Mars there is a china teapot revolving about the sun in an elliptical orbit, nobody would be able to disprove my assertion provided I were careful to add that the teapot is too small to be revealed even by our most powerful telescopes. But if I were to go on to say that, since my assertion cannot be disproved, it is intolerable presumption on the part of human reason to doubt it, I should rightly be thought to be talking nonsense. If, however, the existence of such a teapot were affirmed in ancient books, taught as the sacred truth every Sunday, and instilled into the minds of children at school, hesitation to believe in its existence would become a mark of eccentricity and entitle the doubter to the attentions of the psychiatrist in an enlightened age or of the Inquisitor in an earlier time.”

Let’s start again: William James told the story of a group of hunters in the forest. One of the men sees a squirrel on a tree, and the squirrel sees him. The squirrel scrambles to the opposite side of the tree from the man. The man circles the tree, and the squirrel cautiously stays on the opposite side of the tree from him, and around and around they go, Does the man go around the squirrel? The hunters disagree. One says the man goes around the tree and the squirrel, and another objects that the man goes around the tree, but not the squirrel. They turn to James to get the opinion of a philosopher. “It’s all a matter of defining your terms,” James answers. “If  by ‘going around’ you mean ‘going east, south, west, north, east, etc.,’ then the man certainly goes around the squirrel. But if by ‘going around’ you mean ‘going from side to back to side to belly to side, etc.’ then the man does not go around the squirrel.”

James realized that many disputes are purely verbal and can be cleared up by defining your terms. For example,  If a tree falls in the forest and there’s nobody to hear, is there a sound? And which came first, the chicken or the egg? Defining our terms should help in these cases. But what about this puzzle that Bertrand Russell ran into while working on set theory for Principia Mathematica? In a certain village there is an adult male barber. He shaves all and only those males in the village who do not shave themselves. So, if I live in that village and do not shave myself then the barber shaves me. And if I shave myself then the barber does not shave me.

But what of the barber? Does he shave himself? Well, if he shaves himself then he does not shave himself!! There does not seem to be a term that needs defining here. Shaving is pretty clear. This one seems a genuine paradox. Or, there can be no village with just those properties.

Galileo used a thought experiment to challenge Aristotle’s common sense idea that heavy objects fall faster than lighter objects. Galileo argued against the common sense idea of his time that heavy objects fall faster than light objects – take object A 15 lbs. and B 5 lbs.; according to your claim A will fall faster than B. But if I connect the two together then the combination will at 20 lbs. fall faster than either, but wait B will act as a drag and slow the combined thing down! So, C will fall both faster and slower than itself!! And that cannot be. This move is called a  Reductio ad Absurdum argument.

Consider one of the central myths of philosophy: Plato’s cave. In it Socrates describes this situation: we are all seated in our pews looking out at the world. We notice shapes of animals and vegetables, chairs and tables, and so on,  and believe that we are in touch with reality. But eventually some curious and brave person (a philosopher) breaks free from the restraints and walks out of the cave toward the sun. They notice that what they previously believed to be real was in fact just the shadows of reality – shadows cast on the screen by the light of the sun. Believing that what our senses tell us is the end of the story proves to be problematic. We could be wrong about our beliefs!

How about another DEWM (dead, European, white, male) Rene Descartes? Descartes began his philosophical career by trying to set forth the basic principles of the new scientific method that Galileo had introduced and which had proved so successful. At the same time he wished to show that this new scientific methodology was consistent with Christianity and provided no threat to it. Thus, Descartes had two main aims in the Meditations:

  1. To provide a sound basis for scientific method. He aimed to show that the real source of scientific knowledge lay in the mind and not in the senses.
  2. To show how science and religion could be compatible. He will do this by splitting the world up into two different types of substances: mind and body. Science will be completely true of body, extended matter; religious truths will deal with the soul or mind.
  3. The Arguments for Universal Doubt:

In order to show that science rested on firm foundations and that these foundations lay in the mind and not the senses, Descartes began by bringing into doubt all the beliefs that come to us from the senses. His aim in these arguments is not really to prove that nothing exists or that it is impossible for us to know if anything exists (he will prove that we can know external objects later), but to show that all our knowledge of these things through the senses is open to doubt. If our scientific knowledge came to us through the senses, we could not even be sure that anything outside of us existed. The obvious implication is that, since we do know that external objects exist, this knowledge cannot come to us through the senses, but through the mind.

Descartes uses three very similar arguments to open all our knowledge to doubt: The dream argument, the deceiving God argument, and the evil demon argument. The basic idea in each of these is that we never perceive external objects directly, but only through the contents of our own mind, the images the external objects produce in us. Since sense experience never puts us in contact with the objects themselves, but only with mental images, sense perception provides no certainty that there is anything in the external world that corresponds to the images we have in our mind. Descartes introduces dreams, a deceiving God, and an evil demon as ways of motivating this doubt in the veracity of our sense experience.

  1. The dream argument:
  2. I often have perceptions very much like the ones I usually have in sensation while I am dreaming.
  3. There are no definite signs to distinguish dream experience from waking experience.


  1. It is possible that I am dreaming right now and that all of my perceptions are false

Descartes realizes that someone may not accept that all of the elements of our dreams may be illusory, so he introduces another mechanism to increase the scope of our doubt.

  1. The deceiving God argument:
  2. We believe that there is an all-powerful God who has created us and who is all powerful.
  3. He has it in his power to make us be deceived even about matters of mathematical knowledge which we seem to see clearly.


  1. It is possible that we are deceived even in our mathematical knowledge of the basic structure of the world.

For those who would hold (as Descartes himself will later) that God would not deceive us, Descartes introduces an evil demon instead.

  1. The evil demon argument:
  2. Instead of assuming that God is the source of our deceptions, we will assume that there exists an evil demon, who is capable of deceiving us in the same way we supposed God to be able.

Therefore, I have reason to doubt the totality of what my senses tell me as well as the mathematical knowledge that it seems I have.

Since the source of our knowledge cannot lie in the sense, Descartes must find a way to rebuild the edifice of knowledge upon material he can find within the contents of his own mind. The first thing he can be sure of on the basis of this alone is his own existence.

  1. The argument for his existence (The “Cogito” argument)
  2. Even if we assume that there is a deceiver, from the very fact that I am deceived it follows that I exist.
  3. In general it will follow from any state of thinking (e.g., imagining, sensing, feeling, reasoning) that I exist. While I can be deceived about the objective content of any thought, I cannot be deceived about the fact that I exist and that I seem to perceive objects with certain characteristics. (The famous statement of this from D.’s Discourse on Method is “Cogito ergo sum.” or “I think, therefore I am.”)
  4. Since I only can be certain of the existence of myself insofar as I am thinking, I have knowledge of my existence only as a thinking thing (res cogitans).

This shows that the contents of the mind are more easily known than the body:

The Argument that the Mind is More Certainly known than the Body:

It is possible that all knowledge of external objects, including my body, could be false as the result of the actions of an evil demon. It is not, however, possible that I could be deceived about my existence or my nature as a thinking thing.

Therefore, our mind is much more clearly and distinctly known to us than our body.

Descartes still has no knowledge of anything outside of his mind. He still has to make the crucial leap to the existence of an object outside of his mind. He must do this, however, strictly on the basis of the contents of his own mind. It is the idea of God that he finds in his mind that allows him to make this leap, and which forms the basis for his knowledge of all other external objects.

III. The argument for the existence of God from the fact that I have an idea of Him. (simplified version)

  1. I have an idea of God, a perfect being.
  2. There must be as much reality or perfection in the cause of any thing as in the effect.
  3. This applies not only to the existence of ideas, but also to the reality of what they represent. Not only must the existence of the idea be explained, but also what it represents.
  4. The idea of God represents something so perfect that I could not have been the cause of this idea.

Therefore, God must exist as the only possible cause of the perfection found in my idea of Him.

With the knowledge that God exists and that he is not a deceiver, Descartes can move on to explain how we know material objects to exist.

  1. The argument that material objects exist.
  2. God is no deceiver.
  3. He created me and gave me reason which tells me that my ideas come from external corporeal things.
  4. If they do not come from external objects, then God must be a deceiver. But this is an absurdity.


  1. Material objects exist.

Having put our scientific knowledge on a firm foundation and having shown that it comes from our mind, not our senses, Descartes needs to show how this new type of knowledge is compatible with religion. He has done this, partially by showing how it leads to knowledge of the existence of God. He still has to reconcile the seeming incompatibility in the objective and subjective views we can take of ourselves. He does this by spitting us up into two distinct substances: mind and body.

  1. The argument for the distinction of mind and body.

Each of these arguments depends on Leibniz’s law, which says:

Leibniz’s law: If two things are the same thing, they must share all the same properties.

Descartes shows two ways in which mind and body seem to have different properties, and how, hence, they must be different things.

  1. The argument from knowledge.
  2. I can be certain that my mind exists.
  3. I cannot be sure that my body exists.

Mind and body are not the same thing.

  1. The argument from extension.
  2. My mind is unextended.
  3. My body is extended.

Mind and body are not the same thing.

Since Descartes’ mind/body split science and philosophy have worked to put humpty dumpty back together again, so that today’s reigning theory is the mind/brain identity theory.  Part of Descartes’ motive for the split was to separate science (the physical world) from religion (the world of celestial teapots) so that he could do his science without being persecuted by the Church – as Galileo before him had been.

I tell you about these famous thought experiments in order to remind you of the importance of thinking carefully and with imagination about all human problems. I urge you to celebrate your children and your grandchildren as they challenge and struggle against the accepted traditions and beliefs of our community. And above all to celebrate rational thought and the scientific method as ways of dealing with the most serious of our human problems.

I do this because I am intrigued by the popular slogan “Save the Planet” – for although I understand the idea behind the slogan I find it wrongheaded. The planet will save itself. The planet will flourish without us.

It is humanity we need to worry about.

Let me close by quoting from one of my favourite authors. In a sermon by Kurt Vonnegut jr. he ended by saying:


This has no doubt been a silly sermon. I am sure you do not mind. People don’t come to church for preachments, of course, but to daydream about God. I thank you for your sweetly faked attention.



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