Saturday, November 19, 2011

Does the Scientific Method Employ a Logical Fallacy?

In The Limitation of Bacon's Scientific Method Jacob Schriftman suggests that the scientific method is based on the formal logical fallacy commonly known as "Affirming the Consequent."  If correct, this is an astounding claim.  Could it be that the scientific method is founded on bad reasoning?  In this post I will attempt to explain the suggestion made by Schriftman and then I will share my thoughts on the implications.

Let's begin with the formal logical fallacy commonly known as "Affirming the Consequent."  This fallacy is formal in that the form of the argument is fallacious.  In logical terms the form of this argument is as follows:

1. If p, then q.
2. q.
Therefore p.

In premise (1) p is called the antecedent, and q is called the consequent.  This argument form attempts to show the truth of the antecedent by affirming the truth of the consequent.  In order to show that this form is fallacious we will let p= "it is raining" and q= "my truck is wet."  Now we have:

1. If it is raining, then my truck is wet.
2. My truck is wet.
Therefore, it is raining. 

The problem here is that that there may be other conditions that make my truck wet other than rain.  So that the premises (1) and (2) may true, while the conclusion "it is raining" may be false.  For instance, my truck may be wet because it is being washed on a very sunny day (hence no rain).

One of my favorite examples of "Affirming the Consequent" is as follows:

1. If we have great minds, then we think alike.
2. We think alike.
Therefore, we have great minds.

The fact is, we may both think alike, and be blithering idiots.  In any statement in the form of a conditional (i.e. If p, then q), p will be a sufficient condition for q; while q may not be the only sufficient condition for p.

So what does this have to do with the scientific method?  The scientific method may be (and often is) considered a procedure (i.e. method) for obtaining knowledge about observable phenomena.  In fact, many individuals believe that the scientific method is the only way to truly gain knowledge.  If a knowledge claim is not known via the scientific method, then said claim cannot be known.  Now, if the scientific method is based on fallacious reasoning, then all we claim to know via science is based on fallacious reasoning.

We will remember from our high school science classes that the scientific method begins with a hypothesis concerning some observable phenomena.  Then a prediction is made concerning that hypothesis.  After making the prediction, experiments are carried out in hopes that the prediction will prove accurate.  If the prediction proves accurate, then the hypothesis is verified. A mundane example may help refresh our memories.

Let's assume that I drink hot tea every day (I do not).  I observe that the water seems to boil at the same temperature every time I prepare my tea.  This intrigues me (actually I could care less, but let's continue).  I decide to apply the scientific method in order to gain new knowledge about the temperature at which water boils.  I form the hypothesis that water always boils at the same temperature.  I predict that every time I boil water it will boil at the same temperature.  I perform an experiment by boiling water and checking the temperature at which it begins to boil.  I know that I must do this several times, and I find in each case that water boils at 212 degrees F (Fahrenheit). It seems that my hypothesis is true...right?

According to Schriftman I have come to this conclusion via a fallacious argument.  Let p= my hypothesis and q= my experiments.  In other words p= "water always boils at the same temperature" and q= "every time I boil water it boils at 212 degrees."  Now we have:

1. If water always boils at the same temperature, then every time I boil water it boils at 212 degrees.
2. Every time I boil water it boils at 212 degrees.
Therefore, water always boils at the same temperature.

It seems that I know that water always boils at the same temperature, but according to Schriftman I have come to this conclusion by affirming the consequent.  Is my hypothesis wrong?  Could there be other conditions for my water always boiling at 212 degrees, such that under other conditions water may boil at another temperature?  Yes.  I happen to live at sea level.  At sea level water always boils at 212 degrees.  If I lived on top of Mt. Everest then my water would boil at a lower temperature.  Again, if I added salt to my water it would boil at a higher temperature.

So it seems that Schriftman has a point.  The scientific method seems to proceed by fallacious argumentation.  If the hypothesis is the antecedent and the experiments meant to prove the hypothesis are the consequent, then the scientific method seeks to show the truth of the antecedent by affirming the consequent.

In hindsight this is really no surprise.  Consider the "scientific studies" that we read or hear about in the news.  One study says eggs are bad for my heart (cholesterol).  Another says they are good for my heart (omega-3's).  One study says red wine is good for the heart.  Another study comes out years later which says any wine may contribute to the onset of breast cancer in women.  Obviously, conditions for particular hypothesis continue to crop up that change the conclusions.

At this point some logically astute scientific mind will argue, "The scientific method is not based on the formal fallacy of Affirming the Consequent.  In fact the scientific method is based on the valid argument form known as Modus Tollens."  Science is not attempting to prove the truth of a hypothesis via experiments.  The sole purpose of experiments is to falsify hypotheses.  Let's examine this claim by clarifying the valid argument form known as Modus Tollens:

1. If p, then q.
2. not-q.
Therefore, not-p.

Let p= "it is raining" and q= "my truck is wet."  Now we have:

1. If it is raining, then my truck is wet.
2. My truck is not wet.
Therefore, it is not raining.

This argument form is valid in that if the premises are true, then the conclusion necessarily follows.  The condition given for my truck being wet is rain.  If my truck is not wet (given that condition), then it follows that it is not raining.  In the same way, the scientific method proceeds not by affirming a hypothesis by experiments, but by trying to dis-prove a hypothesis by experiments.  Hence, if p= hypothesis and q= experiments and the experiments do not show what was predicted, then the hypothesis is not accurate.  In short, scientific hypothesis can never be proven true, they can only be proven false.  This is why Einstein said,
  "No amount of experimentation can ever prove me right; a single experiment can prove me wrong."1
All of this seems to place science as a method on very precarious footing.  On the one hand we should all be familiar with these problems from our high school science classes.  We should all be fully aware that scientific hypotheses are just that...hypotheses.  However, this is not how scientific "knowledge" is treated in either the common populace or in the scientific community.  One glaring example is the current experiments concerning neutrinos.  It may be the case that Einstein was wrong and one experiment may prove that he was wrong.  Physicists are praying to their hypothetical universal Being that the findings of the Opera collaboration are wrong.  If the findings are right, then a hundred years of scientific thinking will have to be re-written.  Some folks in the scientific community are acting as if all they know will be turned upside down.  This is amazing for a community who should know that all they can possibly know is what they cannot know.   


  1. Interesting. I agree heartily with the last paragraph that was written. I find it sad that the scientist, who should be the most open of us all to the possibility of a wrong way of thinking being proved wrong, shakes fearfully at the slightest indication that they are wrong. Bravo, sir, for this thought-provoking post.

  2. I personally fear that this very fallacy is a time waster in modern science. We spend much time building on past theories that are eventually proven wrong. Alas, our scientific community is a dogmatic one.

  3. Actually no, In scientific settings all assumptions are explicit and made clear. Nothing is ever claimed to be proven, but instead fairly well substantiated and never disproven - as it is the case of the theory of relativity. And of course those theories cannot be proven true, because they are NOT true. They are models, and models are not the objects they model. They however are useful and are schematics indicative of what is most plausible to be happening. I fail to see that supposed dogma of the scientific community (I see excitement about what is not known, which is the main drive in science - more than the money which highly qualified academics could make more and more easily in the private sector). But I do see plenty of misunderstanding from the common folk.