Problems with Defining Science Using the Falsification Criterion

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This blog is the second entry in a series by Steven Benner. The first post can be found here. Throughout the series, Benner discusses the nature of scientific progress and the difficulty of defining what is and is not science. 


Problems with Defining Science Using the Falsification Criterion

As we began to see in my last post, falsifiability is not a particularly useful tool for distinguishing scientific and nonscientific propositions. Take a simple law-like proposition that philosophers of science like to discuss: "All emeralds are green". We may regard this proposition as scientific because we can conceive of an observation that falsifies it. We might observe an emerald that is not green. Hence, we might conclude that the proposition is "scientific" under the falsifiability demarcation criterion. Not a particularly interesting law, of course. But perhaps we can be satisfied that we are doing "real science".

We can even express this in a syllogism that classical Greek philosophers would recognize (it is called the contrapositive). If an observed X is an emerald and X is not green, then the proposition is false.

Unfortunately, things are not so simple in the real world of science. It turns out that whether or not an emerald is observed to be green depends on how it is observed, and who is doing the observing. For example, an emerald may be observed to fluoresce a red color when observed under ultraviolet light.

No problem, you say.

The proposition can be changed to read: "All emeralds are green when examined under white light". But even then, the falsification effort does not work if the observer has red-green colorblindness. We must further modify the proposition to read: "All emeralds are green when examined under white light by an observer who does not have red-green colorblindness".

These modifications of the original law constitute ad hoc "auxiliary propositions". We invent them to explain away an observation that would otherwise appear to be falsifying. This type of thing seems to defeat the demarcation.

We might say: Fine, scientists are not allowed to modify, ad hoc, propositions so that they survive observations that apparently falsify them. Unfortunately, it is not justifiable. We shouldprotect propositions from certain contradicting observations. For example, we should not discard a theory if the observing instrument was broken at the time that it generated an allegedly contradicting observation.

The creation of auxiliary propositions ad hoc must be done if one does not want to be paralyzed in building models for reality by the exigencies of real world experimentations and observations. Not surprisingly, the history that created the empowerments cited above is littered with ad hoc auxiliary propositions.

These problems become only worse when we move to more complex (and more interesting) scientific propositions, where many propositions are logically connected, including many that we do not even know that we are presuming. For example, it is widely accepted today that the Earth was formed about 4.5 billion years ago and that life has been present on Earth for the majority of the time since it formed.

No problem today, perhaps, but it was a problem in the 19th century as evolutionary theory was being developed. Biologists required hundreds of millions of years of Earth history to explain the observed diversity of life under a model of gradual evolution. Darwin himself used the record of sedimentary rocks to suggest that the Earth was at least 300 million years old.

Some famous physicists disagreed, including the physicist William Thompson, also known as Lord Kelvin. Kelvin was the physicist who helped develop the laws of thermodynamics, one of the most robust sets of laws that physics has ever produced. Kelvin's contributions to physics were so significant that the absolute temperature scale is named for him. We measure temperatures from absolute zero using "the Kelvin", not "the degree Fahrenheit" or even "the degree Celsius".

Starting in 1862 and for forty years thereafter, Kelvin used his understanding of thermodynamics to argue that the Earth could not possibly be as old as evolutionists required. Why? Because the Sun could not possibly be so old. Even if the Sun were made of the best coal possible, said Kelvin, it could produce heat at its current rate for only about a thousand years. Kelvin thus held that the laws of physics disproved the model of common descent by gradual evolution, key to Darwinian evolution as a theory.

Today, we know that the Sun generates its energy by nuclear fusion and radioactive decay, not by burning coal. This involves the conversion of matter to energy under Einstein's famous e = mc2 equation. Kelvin knew nothing of either. Nor, however, did the evolutionists who stubbornly continued to believe in evolution, despite its having been "falsified" by physics. Illustrating the challenge in defining science as a string of falsifiable propositions, Kelvin's falsification had to be ignored to get the correct answer about the age of the Earth.

The exhortations to "think outside the box" or to "challenge authority" do not serve us here. Had we put Darwin and Kelvin on a stage to have a grand debate, they would never have arrived at e = mc2. Indeed, had someone suggested in 1880 that the Earth was very old and the physicists were incorrect because atoms could fuse to give new atoms with a net conversion of matter into energy, they would have been dismissed as heretics by both camps.

I review these examples of abstract and real science to disrupt the comfortable lessons that you may have been taught about "the scientific method". I also want to emphasize the importance of a more sophisticated understanding of processes within science before people make what they think are "scientific" arguments as they argue in the public square. Once this comfortable complacency is disrupted, we can rebuild a more realistic view of how scientists actually generate empowering knowledge about the real world.

In my next post, we will consider cultural factors that influence how scientists do their work.




Benner, Steven. "Problems with Defining Science Using the Falsification Criterion" N.p., 27 Nov. 2011. Web. 20 January 2017.


Benner, S. (2011, November 27). Problems with Defining Science Using the Falsification Criterion
Retrieved January 20, 2017, from

About the Author

Steven Benner

Steven Benner is a Distinguished Fellow of the Foundation for Applied Molecular Evolution in Gainesville, FL. He received his doctorate in chemistry from Harvard University. Benner and his group of researchers initiated synthetic biology as a field and invented dynamic combinatorial chemistry, which is currently being used in pharmaceutical development.

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