Logical Fallacies: Appeal to Ignorance

Does anything sound “off” about the logic in the following dialogue?

Friend #1: We’d better be careful while we’re fishing today; there could be sharks in these waters.

Friend #2: Come on—there aren’t any sharks around here.

Friend #1: How do you know?

Friend #2: Well, I’ve been fishing here for years and I’ve never caught one.

Friend #1: But nobody’s proven that sharks don’t live in these waters, so they must be around here somewhere.

Appeals to Ignorance

In this example, both friends are basing their arguments on a lack of contrary evidence. Friend #1 is claiming that sharks are present because there’s no evidence against them, while Friend #2 is reasoning sharks are absent because there’s no evidence for them. Claiming that a message must be false because there’s no evidence for it or true because there’s no evidence against it: both involve a type of flawed logic called the appeal to ignorance fallacy.

We can catch appeals to ignorance with the critical thinking hack of asking, “Is a message true because . . . ?” In this case, we’d ask, “Is a message true (or false) because there’s no evidence against (or for) it?” Framed this way, it’s easier to see the answer is “not necessarily.” While a total lack of evidence would not give us reason to believe an argument’s conclusion is true, neither would the lack of evidence alone prove the conclusion is false.

Defining the Terms

When discussing the (lack of) evidence for something, it’s always useful to apply Critical Thinking Check #4, Check the Definitions, to clarify what evidence means. As other articles explain, evidence refers to facts from observational science, which measures, tests, and describes things we can observe in the present. Both creationists and evolutionists examine the same evidence. But they interpret it through different worldview lenses to reach different conclusions.

For instance, I remember a professor telling our class, “There is not a single piece of evidence against evolution.” Already, we might notice an appeal to ignorance implied in that statement. But to fully respond, we need to clarify the statement’s keywords.

Take the word evolution. Evolution, in this case, refers to one kind of animal changing into a distinctly different kind over time. And as other articles address in detail, there are plenty of facts from observational science—in other words, pieces of evidence—which cause problems for this idea. Ultimately, the argument that evolution is true because ‘there is no evidence against it’ is both invalid (because it contains an appeal to ignorance) and unsound (because it contains a false premise).

Avoiding Appeals to Ignorance

But you know, I’ve seen creationists being accused of appealing to ignorance too—for example, when discussing the lack of “transitional forms” in the fossil record compared to what Darwin himself would have predicted.1 Evolutionists, including the author of my third-year evolution textbook, often respond that there are plenty of specimens interpreted as “transitional fossils.” (However, you can learn about some of the problems with these interpretations in these articles.) Evolutionists may add that even if there weren’t such specimens, the absence of evidence is not evidence of absence.

Technically, that’s true. The fact that we don’t see definite “transitional fossils” cannot prove transitional forms never existed, just like the fact that we haven’t seen definite human and dinosaur fossils together does not mean humans never lived at the same time as dinosaurs. It just means they weren’t buried together.

Instead of stating that a lack of evidence proves something (especially because science, being inductive, does not conclusively prove conclusions anyway), we can avoid appeals to ignorance by focusing on what the available evidence does support. For example, instead of saying that the lack of fossil evidence disproves evolution, we could point out that the available fossil evidence is inconsistent with many evolutionary predictions,2 but more consistent with what we’d expect to see from a global flood.

Summing Up

Ultimately, a lack of evidence alone provides us neither reason to believe a claim is true nor logical grounds to conclude the claim is false. So, it’s fair to point out an unexpected lack of evidence for something, but not to treat the lack of evidence as a definite disproof. Rather, it’s usually best to discuss whether the facts which we can observe are consistent or inconsistent with a certain conclusion. For example:

Friend #1: We’d better be careful while we’re fishing today; there could be sharks in these waters.

Friend #2: I wouldn’t worry about it. We’re in a freshwater lake system, and studies suggest sharks can’t float well in freshwater.3 That’s why sharks don’t usually invade lake habitats.

Friend #1: Well, that’s nice to know!

See the difference? Known information makes a far sounder basis for belief than does a lack of evidence alone. And conveniently, a biblical worldview supplies a foundation for truly knowing information in the first place. By familiarizing ourselves with solid apologetics information to defend that worldview, we can avoid appeals to ignorance and answer for our hope in Christ (1 Peter 3:15), based not on what we don’t know but on what we do know.