How is Truth Known?

In previous posts (with a helping hand from Norman Geisler and Frank Turek) I’ve shown why I think philosophers like David Hume and Immanuel Kant fail in their attempts to deny the concept of absolute, knowable truth. Showing that Hume, Kant, and their intellectual offspring are wrong, however, does not establish the truth of Christianity. In fact, it doesn’t even take the more basic step of demonstrating how we do come to know truths about the world.

As Geisler and Turek put it, first principles like the Law of Noncontradiction and the Law of Excluded Middle (e.g., either Jesus rose from the dead or he did not, but there is no third alternative) are “tools we use to discover all other truths.” By themselves, however, they cannot distinguish between a claim that is true and one that is false. Take, for instance, the classic syllogism:

All men are mortal.

Socrates is a man.

Therefore, Socrates is mortal.

Even for someone who has never studied logic the final statement is obviously a logical conclusion. That it is logical, however, does not demonstrate that the conclusion is true. We can see this easily simply by tweaking the syllogism:

All men have a third eye in the middles of their foreheads.

Socrates  is a man.

Therefore, Socrates has a third eye in the middle of his forehead.

The conclusion is still logical in the strict, deductive sense, but the conclusion is also obviously false. The truth or falsity of the conclusion, then, depends on the truth or falsity of the premises.

Deduction won’t help us establish whether a particular premise is true. For that, we must rely on induction, the process of drawing general conclusions from specific observations. It’s by the process of induction that we know the first premise in the second example to be false. None of us has seen every human being, but we have seen enough of them to conclude with a high degree of certainty that none of them have three eyes, with one in the middle of the forehead.

Notice that I said we can have a “high degree of certainty” and not that we can be absolutely certain. Each of us has seen many people, but no one can claim to have seen every human being that ever existed. Thus, I can’t say with absolute certainty that there’s not someone out there with a third eye in the middle of his forehead.

Even in the absence of perfect information, however, we still have enough information to, as Geisler and Turek put it, “make reasonably certain conclusions on most questions in life.” That’s why we can trust both the logical validity and truth of the first example above: virtually everyone has been observed to die and, therefore, the conclusion that all men are mortal is true beyond a reasonable doubt, even if we cannot say that it is true beyond all doubt.

The process we use to investigate the world around us is the same process we use to investigate the truth of God’s existence. While it’s true that we can’t observe God directly, we can observe the effects of his existence. Gravity, for instance, is a force, but it is observable only through its effects on other objects. Geisler and Turek also use the example of their book: we almost take for granted that the words we read are an effect produced by an intelligence, a human mind. All of our observation tells us that books are not the product of natural phenomena like gravity, wind, or the random accumulation of cosmic dust.

To summarize, allow me to quote Geisler and Turek at greater length:

Now here’s the big question: Just as a book requires preexisting human intelligence, are there any observable effects that seem to require some kind of preexisting supernatural intelligence? In other words, are there effects that we can observe that point to God? The answer is yes, and the first effect is the universe itself. An investigation of its beginning is the next step on our journey to discover the box top.

Before I proceed in that direction, however, a crucial question to address first is “So what?” The topic of the next post in this series will focus on why truth matters in the first place.



Filed under Apologetics

3 responses to “How is Truth Known?

  1. Great article!

    I’m curious what kind of answer you would give to those who ask “how do you know induction is valid?”

    If it is true that we gain knowledge by a certain method, then we also gain “knowledge of method” by that very same method; so how did we discover the method in the first place?


    • Great questions! To a certain extent I think most people take inductive reasoning as a presupposition; they do it all the time and don’t really give it a second thought.

      I’m not so sure, however, that we can or ought to stop at the “we take it as a presupposition” stage. I don’t have a deeper answer at the moment. But maybe that just makes a good topic for a future post!


      • It’s a tricky question, but I think there are good answers.

        Here’s how I think about it:

        We are able to learn, and in only in retrospect are we able to learn *that we have learned. Only at that point can we ask questions about the method of learning.

        Method only pertains to higher levels of abstraction—not to early-level perceptions and observations.

        A person is not required to know a method before knowing first-level facts. He only learns about method on the basis of his first level knowledge.

        This shows that the chicken and egg challenge is invalid.

        It’s a fascinating topic. I have an essay on it:


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