Logic in Apologetics

by Matt Slick

Logic is typically very important in apologetics. To defend the faith, the Christian must use truth, facts, and reason appropriately and prayerfully. The Christian should listen to objections and make cogent and rational comments in direct response to the issues raised.

Logic is simply a tool in the arsenal of Christian apologetics. Logic is a system of reasoning. It is the principle of proper thinking used to arrive at correct conclusions. Of course, some people are better at thinking logically than others, and there is no guarantee that using logic to the best of one's ability will bring about the conversion of anyone. After all, logic is not what saves a person. Jesus does that, and we are justified by faith (Rom. 5:1).

Therefore, the proper use of logic in apologetics is to remove intellectual barriers that hinder a person from accepting Jesus as Savior. Logic is not to be looked at as the answer to every problem facing Christianity nor every objection raised against it.  Logic has its limits. It cannot guarantee wisdom. It cannot prove or disprove inspiration or love.  It cannot replace the intuition gained through experience, the prompting of the Holy Spirit, nor the clear truth of God's word.  Nevertheless, logic is still very valuable and can be quite powerfully used by people--both saved and unsaved.

Opponents of Christianity use logic

Sometimes an opponent of Christianity might use logic problems as a type of evidence against God’s existence. Consider this rather basic objection:

  • Proposition: God can do all things.
  • Statement: Can God make something so big that He cannot pick it up? If He can, than He cannot do all things because He could not pick up the rock. If He cannot, than He cannot do all things because He cannot make a rock so big He can’t pick it up.
  • Conclusion: Since God can do all things and we have shown that there are things He cannot do, therefore, God does not exist.

On the surface, this logic could be difficult to answer. But, all we have to do is think a bit more, and we can see that the problem asserted above is not logical to begin with. Here's the answer:

  • Proposition: God cannot violate His own nature; that is, He cannot go against what He naturally is.
  • Statement: God's nature does not permit Him to lie, to not be God, etc.
  • Conclusion: Therefore, the statement that God can do all things is not true, and the conclusion raised against God is also not true.

Logic is a valuable tool in witnessing particularly when using proofs of God's existence.  Consider the following basic approach using logic:

  1. The universe exists.
  2. The universe cannot be infinitely old; because if it were, it would have entered into a state of entropy long ago.
    1. Entropy is the second Law of thermodynamics which states that all things are moving toward chaos and non-usable energy.  In other words, everything is running down.
  3. The universe is not in a state of non-usuable energy; therefore, it is not infinitely old.
    1. If the universe were infinitely old, the universe would have run out of usable energy long ago.
  4. Since the universe is not infinitely old, it had a beginning.
  5. The universe could not have brought itself into existence.
  6. Something before the universe and greater than the universe had to bring the universe into existence.
  7. That something is God.

All logical proofs for God have strengths and weaknesses.  But the Christian should not be afraid to use logic, reason, and evidence when defending the faith.

I suggest getting books on introduction to logic and go through what you can.  Absorb as much as possible.  Also, learn to ask questions in discussions.  Learn to think about what the ramifications are of what people are saying.  Look for logical flaws in their speech and your own.  If it helps to learn from actual dialogues, go to the Apologetics Dialogues page and read some of the actual dialogues I've had with unbelievers.  They should help to see how to "do apologetics" though I have much to learn in this area.

Is logic a common ground between the believer and the unbeliever?

Some state that there is no common ground between the believer and the unbeliever, and that the unbeliever's initial presuppositions against the Christian God do not allow him to accurately reason concerning God, the world, truth, or himself. Therefore, some Christian theologians conclude there can be no ultimate common ground because the unsaved are unregenerate, and their presuppositions are opposed to true rationality.

"Logic is true--not because it is logical but because it is a reflection of God's nature, which is order and truth."

I believe that logic is indeed a type of common ground. But I do not believe that it possesses some innate quality that renders it above human capacity or limitations, nor does it possess any ethereal, mystic qualities that somehow transcends the blinding influence of sin. I think that logic, used properly, always vindicates the truths found in the Bible and points to God--whether or not an unbeliever acknowledges it.

Logic belongs to God. This is so because God has invented the universe, the physical laws, mathematics, and all other natural and true phenomenon in it. Existence has an order because God gave it order. Logic is true--not because it is logical but because it is a reflection of God's nature, which is order and truth. Therefore, logic ultimately belongs only to God and can only properly be used by Him and in matters pertaining to God by the Christian.

This is not to say that an unbeliever cannot master the logic, say of mathematics, better than a believer. There are areas of knowledge common to both, and God has given some people abilities not possessed by others. However, this not an assertion that all Christians, when speaking of God, do so flawlessly.  Many Christians are very illogical when they try to defend God.

The fact is that no one can claim to have ultimately mastered logic. In a perfect world with unfallen people, reasoning would be a marvelous adventure that would lead us to more of God's revelation and truth.  But we don't live in a perfect world.  We live in a fallen world where sin has influenced not only our bodies, emotions, and wills but also our minds.

Is logic enough?

Is logic enough for the Christian? No, it isn't. Logic has two major flaws: First, it is only as good as the one who is using it (though that really isn’t a flaw in logic). Second, logic doesn't save. Jesus does. We cannot reason someone into the kingdom of God. It is the Holy Spirit who convicts of sin and righteousness and who opens the heart to understand the truth (John 16:8).

But if that is true, then should we even bother to try to reason with unbelievers? Absolutely, yes, and for several reasons:

  • We are commanded by God to give an answer to unbelievers (1 Pet. 3:15) and to reason (Isaiah 1:18).
  • God can, in His sovereignty, use our witness and reasoning to bring someone into the Kingdom. He is not limited by our inadequacies.
  • Answers that are in agreement with God's word and given to unbelievers, even if they are rejected, are still true answers. The unbeliever will be held accountable on judgment day for rejecting those truths.


Logic is a tool for the Christian. It is nothing to be afraid of. In fact, if you accept the truth that logic "belongs" to God, then you should be encouraged to use it. But, don’t let it become an idol, that is, it is not the answer to the problem. As Christians, we need to use logic as well as evidence, prayer, God's word, love, kindness, etc., in our efforts to win people to Jesus. Reasoning has a valuable place in apologetics and with the believer. It is worth doing well. But use it with love, prayer, and patience.


About The Author

Matt Slick is the President and Founder of the Christian Apologetics and Research Ministry.