It is often said that science is incapable of arriving at certainty because science is based on inductive reasoning, and the conclusions we come to using inductive reasoning are probabilistic, not certain. For example, I could reason that since every crow I have ever seen has been black, that all crows are black. This is probable given our observations, but this conclusion is not certain because it is possible that there are crows of a different color that we have not yet observed.

The history of science has demonstrated just how fallible inductive reasoning is. Many scientific conclusions have proven to be wrong as new data comes to light. For this reason, science is incapable of speaking with any level of certainty to the question of God’s existence. Inductive reasoning simply cannot tell us anything conclusive about God’s existence.

Philosophy, on the other hand, works primarily on deductive reasoning, and deductive reasoning does provide us with certain conclusions. For example, I might reason that

Premise 1 Socrates is a man

Premise 2 All men are mortal

Conclusion Therefore Socrates is mortal.

The conclusion is absolutely certain. Sound philosophical arguments for God’s existence, then, can provide us with certainty about God’s existence. But do they?

While the conclusion of a valid deductive argument is certain, we can only be as certain of the conclusion as we are certain of the premises that support the conclusion. It turns out that the premises in a deductive argument are themselves derived from inductive reasoning or experience, both of which can be mistaken. In other words, deductive arguments provide sure conclusions to probable premises. In the example above, premise two is an inductive conclusion based on our experience with other humans. We have observed that all human beings are mortal, and thus conclude that all human beings are mortal. But it could be the case that there are humans who are immortal that we do not know about. Maybe they live on other planets or in another realm of reality. Granted, the chances of this are slim, but we cannot be certain. The degree to which we can be certain that Socrates is mortal, then, is the degree to which we have reason to believe all men are mortal.

So contrary to popular conception, deductive arguments do not provide certain knowledge. They may provide us with more assurance than inductive arguments, but no argument can provide us with certain knowledge. All knowledge is probabilistic in one sense or the other. While philosophical proofs for God’s existence are vastly superior to inductive proofs, neither can provide us with certainty on this important question.