It is fairly common knowledge that science requires observations and repeatability, but at a quick glance, many fields of science seem to lack those criteria. For example, forensic science, archaeology, and paleontology all deal entirely with past events that can’t be repeated and were not observed. This has led to the widespread misconception that science cannot tell us what happened in the past. Creationists such as Ken Ham have championed this notion as evidence that evolution does not meet the standards of science. He has famously argued that there are two forms of science: observational and historic. According to him, observational science is what we do when we examine current phenomena. So chemistry, physics, most of biology, etc. all count as observational science where we can directly observe what is happening and repeat our observations in laboratory experiments. In contrast, he argues that historical science deals with past events that were not directly observed, and observational science is true science and can be trusted, whereas historical science is, at best, weak and highly unreliable. As I shall demonstrate, however, this distinction is a totally fictitious one that creationists created to support their position. In reality, all science relies both on observations and logical deductions.

I want to begin this post with an example. Consider the following hypothetical situation:

Mary Smith is murdered, and her body is found with stab marks that indicate an unusually curved knife. Fortunately, there is an eye witness who quickly pegs Mark Williams in a lineup. The witness swears that he saw Mark murder Mary, then load her into the trunk of a very dark green car. There is, however, a problem. Mark has an alibi. Credit card receipts confirm that he was several hours away when the crime was committed. Further, Mark didn’t know either Mary or anyone in her family and he has no priors and no motive. Additionally, during the investigation, police discover that Mary’s husband (John) drives a very dark blue car and his trunk has Mary’s hair and blood in it. Further, in John’s laundry, they find a shirt soaked in Mary’s blood, and in his trash they find an unusual knife that is covered in Mary’s blood and John’s fingerprints. Also, the curvature of the knife matches the wounds on Mary’s body. Finally, John has no alibi and he will receive a substantial amount of money from Mary’s life insurance. Who murdered Mary?

If you said John (as any reasonable person would), then you have just affirmed that not only can science answer questions about the past, but evidence based deductions about past events are actually superior to direct observations of those events. This really shouldn’t surprise anyone. Eyewitnesses are notoriously unreliable. To be clear, they aren’t lying. They are describing what happened to the best of their ability, but the reality is that both our perception and memory of what happened can be easily influenced and biased by numerous factors which ultimately render our observations unreliable.

With that example in place, let’s return directly to the topic of observational vs. historical science. First, I need to explain what scientists mean when they say that something is observable and repeatable. In science, we do not use these terms to mean that an event itself was observable and repeatable, rather, we mean that the event left behind observable clues and the methods that we used to examine those clues are repeatable. In other words, if someone else did the same experiment/analysis that you did, they should get the same results. So, in my crime example, the investigators who solved the case did not repeat the murder, nor did any of them directly observe it. Rather, they observed the clues left behind by the murder, and any other investigator who questioned them could have looked at the same evidence and repeated what they did.

This is the same way that we tell what happened millions of years ago. We observe the clues left behind and use those to draw logical conclusions. Usually, we also accompany these observations with exclusive, falsifiable predictions that we can test. In other words, we might make a hypothesis that, “if and only if X happened, we will find Y.” We can then test that hypothesis by seeing whether or not we find Y. The more exclusive predictions that X gets right, the more likely it is to be true. Further, all it needs is one exclusive prediction to fail for X to be rejected. So, in the case of evolution, the theory makes numerous exclusive predictions about genetics, the fossil record, biogeography, etc. We have then tested those predictions by looking at the clues that were left behind, and we have very consistently found that its predictions are true. Also, this process is repeatable, because any other scientist can do the same tests that we did and look at the same evidence that we looked at. So contrary to what Ken Ham would have you believe, we can use science to tell what happened in the past.

The final thing that I want to do in this post is demonstrate that even sciences that Ken Ham considers to be “observational” actually work exactly the same way as his “historical” sciences. For example, no one has ever observed how the inside of the sun works, nor has anyone replicated it in the lab, but we have a very good understanding of how it works, and astrophysics should, by any reasonable standard, be considered observational. So how do we know how the sun works? It’s really quite simple, we made hypotheses about how it works, then we made testable predictions about what should be true if those hypotheses were correct (e.g., what its emissions should be like). Finally, we carefully tested those predictions and used the data from those tests to draw a conclusion about our hypotheses. This is the same exact procedure that we use for fossils.

So maybe astrophysics isn’t an “observational” science, but surely the rest of physics is fine, right? Actually not so much. Take gravity for example. No one has ever observed or replicated gravity. Rather, what we observe and replicate are the effects of gravity. When you watch an object fall, you aren’t seeing gravity, you are seeing its effect. From that effect, we infer the nature and existence of gravity, but we cannot actually observe gravity itself. So according to Ken Ham’s definition, the theory of gravity should not be trusted because it came from the weak, non-observational type of science (gravity is of course also supported by rigorous mathematics).

Chemistry presents a similar problem. No one has ever seen two atoms combine to form a molecule. It has never been observed, but we understand how it works by conducting experiments, measuring the things which can be observed, and using those measurements to deduce how the atoms are behaving. So it is entirely possible to be very certain about how something functions without directly observing.

Finally, what about biology? I’m a zoologist. I study living animals, that has to be observational right? Not really. My studies often rely on logical inferences rather than direct observations. For example, I have published several diet studies in which I collected wild animals, forced them to regurgitate or defecate, then examined what came out and used that information to determine what they had eaten. So, for example, on several occasions I have documented novel prey items for snakes (i.e., they regurgitated a prey item that had never before been documented for that snake species). I did not directly observe the snake eating that prey, but I can infer that it did based on the fact that the prey item was in its stomach. Further, it would be absurd for someone to say, “you can’t actually know that the snake ate that item because you didn’t see it happen.”

So you see, all science is a combination of direct observation and logical deduction. There is no difference between observational science and historical science because we use the exact same methods for each. Science works simply by making and testing predictions. As long as past events left clues behind, we can make predictions about those clues, and test those predictions in order to determine what happened in the past. So the idea that science cannot tell us about past events is absurd and, once again, illustrates just how little creationist groups like Answers in Genesis actually understand about science.