When engaging believers, one is often confronted with the one of the following claims: “you have faith that the sun will rise tomorrow,” or “you have faith that your chair will hold you up when you sit on it.” The purpose of these kinds of accusations is to equivocate between two levels of uncertainty, pulling them both under the umbrella of “faith,” and thus to open the skeptic to the possibility of accepting the superstitious claims of the believer. In order to explain why this tactic is wrongheaded at best, and downright disingenuous at worst, I should first explain a few things about probabilistic reasoning.
Our beliefs do not fall cleanly into a dichotomy of certainty. We are not either 0% certain or 100% certain of a proposition. The certainty of our beliefs distributes on a continuum from 0 to 100% (or 0 to 1, whichever scale you prefer). I may be only 60% certain of the directions to a certain pizza place, but if I consult a map, having gained more evidence, I can increase my certainty to perhaps 99%. That’s what evidence does: it increases or decreases your certainty in a proposition (falsifying evidence decreases it).
Now, I have lots of evidence that the sun will rise tomorrow. I’ve seen it rise over 10,000 times, and I understand the deterministic laws of physics. Very strong evidence exists that it will rise tomorrow. I can probably assign a 99.99999…% certainty to that belief.
On the other hand, I don’t a high degree of certainty that God exists. I haven’t seen any evidence to establish a belief in God. Without any evidence, our certainty in a proposition should be 50% — that is, the proposition is as likely as it is unlikely. And in the case of the Christian God, my certainty is actually less than 1%.
The believer takes any certainty less than 100% as “faith” and equates them. Since you’re not 100% sure the sun will rise tomorrow, and you’re not 100% sure that God exists, your beliefs (or lack thereof) are both based on faith and are equivalent. I think you can see now why this reasoning is erroneous. A certainty of 99.999% is not equivalent to a certainty of 70%, or 50%, or 10%, or less than 1%.
Now, I said that without any evidence one way or another, our certainty should be 50%, but that my certainty of the Christian God is less than 1%. How is this so? In order to explain that, let me use an example.
Let’s say we’re in a public square surrounded by many people. You pull a man out of the crowd and ask me if he is an insurance salesman. Let’s say that I already know insurance salesmen constitute 10% of the general public (yes, I know that number is inaccurate, but let it suffice for the example). I would then have to say that I’m only 10% sure that the man in question is an insurance salesman. I have no other information, and our certainty when randomly pulling someone off the street should reflect the background probability.
Let’s say that you further ask if I believe he is an insurance salesman and a father. I know that 60% of adult men are fathers. I would have to tell you that I’m only 6% sure that he’s an insurance salesman and a father (.10 x .60 = .06).
You see, every time you add another proposition, you have to multiply the probability of each proposition being true together, so the probability decreases. If you claim that a vague “god,” “prime mover,” or “universal energy” exists, without defining the concept any further, I can say I have 50% certainty in that claim. But if you start enumerating a set of characteristics for that God — without any other evidence — my certainty in that exact God decreases.
The Christian God is described in great detail in the Bible. How certain can I be of a God who created the universe is six “days,” who created two people named Adam and Eve, who sent a flood, who dispersed the people of the earth after an incident at the Tower of Babel, who made the Israelites his chosen people, who sent 10 plagues against the Egyptians, who gave Moses a set of 10 commandments inscribed on two tablets, who impregnated a virgin, who took the form of a demigod named Jesus, who walked on water, who fed a multitude with a loaf of bread, who died on a cross, who rose from the dead, who… Well, you get the picture.
With all those propositions about the Christian God, my certainty in that exact god is way, way less than one percent.
Which is a lot less than 99.9999…% — my certainty that the sun will rise tomorrow.
So yes, I’m not 100% certain that the sun will rise. QM theory tells me that there’s something like a 1 in 10^500 chance that all the particles in the sun will vanish overnight. So at best my certainty in the sun rising is only 99.999…% taken to 499 decimal places. But that’s a lot more than my certainty in the Christian God, and they are not equivalent.
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