Two Types of Reasoning

Just for an experiment one day, I tried typing the keywords prove and evolution into my search engine and hit enter. Among the search results, I spotted headlines like, “Three Pieces of Evidence That Prove Evolution Is a Fact.” The article talked about animal similarities, fossil “hominids,” artificial selection, and “vestigial organs,” drawing evolutionary conclusions about the relevant pieces of evidence.

Pieces of evidence are facts from observational science, and facts don’t speak for themselves.

Of course, pieces of evidence are facts from observational science, and facts don’t speak for themselves. They have to be interpreted, and different scientists starting with different worldviews can use different assumptions to construct different interpretations about the same facts.1 This is possible thanks to a type of logic called inductive reasoning, or induction.

To see whether science can really “prove” things, let’s take a closer look at how induction works, and how it compares with another form of reasoning called deduction. By understanding the difference between inductive and deductive reasoning, we can equip ourselves not only to avoid being taken in by overstatements about what science can do but also to recognize certain types of flawed logic—and false teaching.

Inductive vs. Deductive Reasoning2

Induction involves piecing together little facts that we already know to try constructing a larger picture of reality that we don’t already know.

Induction involves piecing together little facts that we already know to try constructing a larger picture of reality that we don’t already know. It’s like beginning with a few puzzle pieces and trying to imagine how the rest of the puzzle might look. On the other hand, deductive reasoning involves looking at a known big picture of reality and drawing smaller conclusions from it. It’s like starting with a puzzle that is already put together, so we can look at little pieces in it knowing where they fit within the bigger picture.

For an example of how deductive reasoning works, let’s say our big picture is a dinosaur. From that known big picture, we could conclusively draw little facts—little pieces of the bigger puzzle—like the dinosaur’s tail, feet, or toes. We already know that these are smaller parts of a dinosaur. So, with deductive reasoning, we could argue,

All dinosaurs have toes.
T-Rexes are dinosaurs (big picture).
Therefore, T-Rexes have toes (little detail).

We know what the big picture (dinosaur) looks like, so we know what the little facts (toes) look like too. Reasoning from big picture to little fact this way is sound logic. Inductive reasoning, however, might argue,

All dinosaurs have toes.
T-Rexes have toes (little detail).
Therefore, T-Rexes are dinosaurs (larger picture).3

This might sound pretty smooth if you say it really fast while standing on your head. However, the problem with inductive reasoning is that little pieces aren’t always enough to lead us to the right big picture. For example, we could inductively argue,

All dinosaurs have toes.
Kittens have toes.
Therefore, kittens are dinosaurs.3

No matter how many little facts, measurements, and observations we have, we can never be sure we’re constructing the right big picture from them, because we can’t know everything.

As cool as dino-kittens might be, the point is that induction doesn’t always work. It’s logically fallacious!4 But you know—historical (or origins) science is based on inductive reasoning.5 So, historical science can be ultimately fallacious. Sure, with enough details and data points, we can use the scientific method (which by the way, is based on deductive reasoning and was formulated by the creationist Sir Francis Bacon) to reach a pretty reasonable conclusion. But in historical science we can’t repeat the past and necessarily prove that our conclusion is the absolute truth. That’s why one of the first things I learned in my science classes was never to write prove on a lab report, even though we often read words like prove in the media.

No matter how many little facts, measurements, and observations we have, we can never be sure we’re constructing the right big picture from them, because we can’t know everything. We may piece together facts until we think we have a good idea of what the larger puzzle looks like, but the next day, another piece of evidence might come along and throw off our whole interpretation.

Deduction and the Bible

Scripture is our only sure starting point for reasoning about how the pieces of the world around us fit together.

Fortunately, there is Someone who already knows everything—Someone who has absolute knowledge of how all the pieces fit together because he created the puzzle. And He’s given us a puzzle box that shows us the big picture of reality through his word, the Bible. That’s why Scripture is our only sure starting point for reasoning about how the pieces of the world around us fit together.

Beginning with God’s Word as our big picture of truth, we can deductively reason that the little statements Scripture contains—including, “in six days the Lord made the heavens and the earth, the sea, and all that is in them”6—are also true. Deducing our ideas from the big picture of Scripture is the proper way to interpret the Bible, a method called exegesis. Often, however, false teachers take individual Bible verses (little details) out of context to inductively construct their own larger pictures of theology, a faulty method called eisegesis.

Ultimately, by recognizing the difference between using induction to inject one's personal beliefs into the text (eisegesis) and using deduction to look at the Bible as a whole and compare Scripture with Scripture (exegesis), we can recognize that real truth is grounded not in fallible human interpretations, but the infallible word of God.

For more on how to think critically about any faith-challenging message, stay tuned for future blog articles and my new video series, CT (Critical Thinking) Scan, available now on the AiG Canada YouTube channel and the AiG Canada Facebook page.