Absence of evidence is not evidence of absence … Or is it?

You might have heard this clever wordplay about how the fact that there is no evidence for something does not mean that this does not exist. People proclaiming “Absence of evidence is not evidence of absence” want to say that just because humans have not found evidence for something, it is not excluded that this does not exist.

Well, yes, it is not excluded, but evidence can be used to infer the presence or not presence of something. “For instance, if a doctor does not find any malignant cells in a patient, finding nothing is evidence of absence of cancer, even though the doctor has not actually detected anything per se.” – Wikipedia

As this shows us, the evidence is one thing and PROOF is another thing. We are not talking about proof here. Do NOT confuse evidence and proof. The proof is a difficult thing and it’s almost always close to impossible. Proof only really exists in mathematics. Evidence, however, does give reason to SUSPECT absence, to consider absence very, very, very likely. So, what’s all this with evidence of absence?

There is always a small, minuscule possibility that the evidence has not been observed yet, but this doesn’t mean that this possibility can and should be used to hang on to outrageously unlikely beliefs. Just the opposite.


Image by stevepb / Pixabay. Public Domain.

When analysing an idea to decide what evidence is necessary to support it, we should always take into account what evidence should be there and how much of it should be there. If there should be a LOT of evidence for something and we know exactly what the evidence should be, then a lack of this evidence does indeed allow us to dismiss this idea.


Scientific Theory

Making sure to avoid any confusion about what "scientific theory" in context of evolution means, Richard Dawkins in The Greatest Show on Earth: The Evidence for Evolution wrote:

Evolution is a fact. Beyond reasonable doubt, beyond serious doubt, beyond sane, informed, intelligent doubt, beyond doubt evolution is a fact.

- Richard Dawkins


What I'm guessing he meant is: evolution did happen and it's still happening. This is proven and solid. Evolution also uses and incorporates other facts that support the conclusion that evolution did happen. In this sense, evolution is a scientific theory and it is supported by facts. And of course, it is true and should be universally accepted as the truth. Creationists would not agree with this, but I would say this doesn't really matter to educated people.

But still, a lot of people say things like "that's only a theory", "why should we base our lives on a theory?, etc when they're talking about evolution, for example. Yeah, like a belief in a sky-wizard is something to base your life on? But I digress - the point of this brief post is just to share a understanding about what scientific theory is.

First thing you'll notice about scientific theories is - there's really PLENTY of evidence for them. This very fact makes them different from what we usually mean when we say "Theory" in normal speech.

Triceratops mounted skeleton at Los Angeles Museum of Natural History, Los Angeles, United States of America, by Allie_Caulfield Derivative: User:MathKnight - File:LA-Triceratops mount-1.jpg (by Allie_Caulfield), CC BY-SA 3.0, Link

By using words such as "FACT", instead of "theory" Dawkins does not confuse people that might not be familiar with scientific meaning of the word "theory" and sometimes I wish other scientists would do the same when talking to the public, just to hammer the point more clearly. If you read Dawkins' quote again, there's no second thought about what he meant evolution is.

Let's not get tangled in words too much, but get right into the point about evolution and other well established scientific theories. So, what does actually mean when a scientist says something is a "scientific theory"?

Well, if you simply ask Wikipedia, it will tell you:

A scientific theory is a well-substantiated explanation of some aspect of the natural world that is acquired through the scientific method and repeatedly tested and confirmed, preferably using a written, pre-defined, protocol of observations and experiments. Scientific theories are the most reliable, rigorous, and comprehensive form of scientific knowledge.


Basically, when scientists use word "theory", they are talking about something completely different than what general public understands under "theory". When you use word "theory" in everyday speech, you actually mean "hypothesis" or "conjecture", something not tested or proven. When scientists use this word, they mean almost the same thing Dawkins meant: That what you and I mean by "fact" in normal speech.

To make an additional point, here are some scientific theories:

  • Special Relativity
  • General Relativity
  • Plate Tectonics
  • Evolution by natural selection
  • Information theory

All these theories have stood the test of time, fought-off challenges, have practical effects and are well-proven pieces of knowledge humanity has. So, don't be fooled by the words and cheap arguments that something is "only a theory". But do be critical and do try and see for yourself. A good rule of thumb would be: if there's evidence for something, it's on it's way to being true and if a idea doesn't have any evidence but requires "faith" or "trust" from you, or only focuses on trying to find flaws in competing idea, it most likely isn't true.

Few Facebook pages to like

We mostly use Facebook to get in touch with our friends, colleagues and family and in this regard we can say that Facebook can be very very helpful. Also, it's fairly low-risk for a woman to tell how to find her on Facebook, instead of giving the phone number. And ... that's about the limit of Facebook usefulness. Or is it?

Below is a list of few pages that I find interesting and "like-worthy".

NASA - National Aeronautics and Space Administration

Bill Nye The Science Guy

Discovery News