I asked our Czech colleague Lukáš Novák for examples of philosophical propositions that he considers to be not only true, but knowable with certainty. He provided this list:
a) God exists.
b) There are substances.
c) There are some necessary truths, even some de re necessary truths.
d) Human cognition is capable of truth and certainty.
e) There are no contradictions in reality.
In this entry I will discuss only the first example.
Is it certain that God exists?
My position is that it is true that God exists, but not certain that God exists. How can a proposition be true but not certain? Logically prior question: What is certainty?
We first distinguish epistemic from psychological certainty. If S is epistemically certain that p, then S knows that p. But if S is psychologically certain that p, i.e., thoroughly convinced that p, it does not follow that S knows that p. For people are convinced of falsehoods, and one cannot know a falsehood, let alone be epistemically certain of it. There was the case not long ago of the benighted soul who was convinced that Hillary Clinton was running a child-abuse ring out of a pizzeria. He was certain of it! This shows that we must distinguish subjective or psychological certainty from objective or epistemic certainty. Epistemic certainty alone concerns us.
But what is epistemic certainty?
On one approach, a proposition is epistemically certain just in case it is indubitable. By indubitability I don't mean a psychological inability to doubt, but a property of some propositions. For example, the proposition I exist has the property of being such that no subject S who entertains and understands this proposition can doubt its truth. There are any number of propositions about one's state of mind at a given time that are epistemically certain to the subject of these states. Examples: I seem to see a tree (but not: I see a tree); I seem to recall first meeting her on a April 2014 (but not: I recall meeting her on 1 April 2014).
The facts about one's mental life are a rich source or epistemic certainties. But there is also a class of truths of reason that are epistemically certain, for example propositions true ex vi terminorum, e.g., every effect has a cause, and formal-logical truths such as a proposition and its negation cannot both be true, etc.
God exists, by contrast with the members of the two classes just mentioned, is not indubitable. One can easily doubt it. Atheists go so far as to deny it. So if epistemic certainty is defined in terms of indubitability, then God exists is not epistemically certain.
We also note that God exists does not record a fact about anyone's mental life, nor is it true ex vi terminorum. So it belongs to neither class of the epistemically certain.
At this point one might respond that God exists, while not indubitable by itself, is indubitable as the conclusion of an argument. Well, suppose you give a valid deductive argument for the proposition that God exists. The conclusion will be epistemically certain only if each premise of the argument is epistemically certain. But is there such an argument?
I don't believe there is. I am, however, quite willing to change my view if someone could present one. Indeed I would positively love to be refuted on this point. After all, I have already announced that I believe it is true that God exists; if it is absolutely epistemically certain, then all the better! To get a feel for the problem, consider the Kalam argument
1) Whatever begins to exist has a cause;
2) The universe began to exist; Therefore:
3) The universe has a cause. (And this all men call God.)
This is a valid deductive argument and the premises are highly plausible. What's more, they may well be true. But they are not both certain. Is (1) epistemically certain? No. Its negation, Something begins to exist without a cause, is not a formal-logical contradiction. Nor is (1) an analytic or conceptual truth.
If an argument is presented for (1), then I will show that the premises of that argument are not, all of them, certain.
Patrick Toner tells me that the "modal ontological argument [is] compelling," and that we can "know God and the soul with certainty through the use of natural human reason." (emphasis added) In Is the Modal Ontological Argument Compelling?, however, I return a negative answer by showing that the crucial possibility premise is not certain.
An impressive argument, no doubt, but not rationally compelling or such as to deliver epistemically certain insight into the truth of its conclusion. The same goes for another powerful argument, From the Laws of Logic to the Existence of God.
What say you, Professor Novak? Can you show me that I am wrong? I would be much obliged if you could.
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