Philosophy Of Science For The Physical Therapist

In The Demon-Haunted World: Science As A Candle In the Dark, Carl Sagan provides an economical definition of science that will be useful for us to start with.  According to Sagan, science is simply “a way of thinking” (25).  As the title of his book would suggest, science is our candle in the darkness that helps us see and understand the world.  Despite the simple definition, there are many values and aspects of science that make it as successful as it is.  And to anticipate charges of elitism, science surely is not perfect.  Science makes mistakes, its conclusions are tentative, and the process is difficult.  But as Sagan points out, science is the best instrument we have for the attainment of knowledge.

The status of science as a knowledge-producing institution in our society is debated by academics in various disciplines, philosophers, and the scientists themselves.  In our field of physical therapy, and sometimes medicine more broadly, science does not have the purchase it ought to have.  Philosophers of science and scientists themselves offer much to learn that will be useful for physical therapists.  When we are immersed in the darkness and uncertainty that we often face in the medical professions, sometimes all you need is a candle.

The Demarcation Problem

It has proven historically difficult to determine what distinguishes real, genuine science from pseudoscience.   The demarcation problem refers to this very question:  How can we tell what is science and what isn’t?  That is, what criteria demarcates science from pseudoscience?  Philosophers have not yet agreed upon an answer but for the scientists in the lab and in the field, this debate has not been of consequence.  However, some of the proposals have utility for the science consumer, i.e. you!  Let’s explore some of the suggested answers.    

Karl Popper originally proposed the idea of “falsifiability, or refutability, or testability” (Curd, 7).  That is, the status of a scientific theory is determined by its ability to be tested.  For any given scientific theory, it must make some sort of prediction that can be settled via some experiment.  If a theory is irrefutable, what arguments can you bring forth against it?  Popper illuminates this criterion with the example of astrology.  Astrologers regularly make predictions about the characteristics of a person and the course of their lives.  However, these predictions are vague enough where any evidence to the contrary can be quickly explained away and belief in astrology can be preserved.  Astrology is unfalsifiable, and thus pseudoscientific.  The success of a theory is thus not rooted in its ability to explain things but its ability to stand up to scrutiny and come out unscathed.  A theory is scientific only if it can be put to the test.  

Despite this useful criterion, many philosophers have suggested that this requirement is not sufficient to solve the demarcation problem.  Paul Thagard has proposed another set of conditions under which we can distinguish real science from pseudoscience.  Thagard proposes a theory can be considered pseudoscientific if it is “less progressive than alternative theories over a long period of time, and faces many unsolved problems’ but the community of practitioners makes little attempt to develop the theory towards solutions of the problems, shows no concern for attempts to evaluate the theory in relation to others, and is selective in considering confirmation and disconfirmations” (Curd, 32).  In short, a theory is pseudoscientific if it unsuccessful and there is no effort to change it from the people that believe it.  While there is still considerable debate among philosophers of science on the demarcation problem, the proposed solutions are useful things to keep in mind for physical therapists.

Distinguishing science from pseudoscience is of vital concern for us, considering health care is often infiltrated by “treatments” that are often not on firm scientific ground, but are presented as such.  As you have seen from previous posts, there will always be a new treatment based on something that sounds scientific.  It will have its enthusiastic and confident purveyors as well as a bunch of satisfied patients.  We need to be able to sift through the noise by ensuring that we put our theories to the test, and having a set of criteria under which you can admit your theory was wrong.  For a given hypothesis or theory in physical therapy, consider a few things; what evidence could be brought forth that would show you are wrong, how successful has it been in the past, and what is the community’s attitude towards the evidence?  If your goal is simply to help people, then science is your ally.  It will put your beliefs to the test, and subsequently do one of two things.  Science will either keep you going on the right path, or help you refocus your efforts.  In both scenarios, you win.  

Attacks On Scientific Realism

Some philosophers debate the very nature of science itself and what it actually seeks to do.  Scientific realism is the notion that the world is in such a way, and science is the enterprise that discovers it.  That is, there are real, discoverable facts about the way the world is, and it’s a scientist’s job is to uncover them.  In addition, scientific realists posit that the progression of science marches us closer and closer to the truth, instead of just finding more useful ways of doing things.  While this theory has gotten some pushback among philosopher’s circles, it stands as a useful starting point for a healthcare professional.  We need to all agree that the world is, in principle, explainable, and there is no magic or miracles that escape our understanding.  If we admit this, than we know that we ought to look to science for a serious attempt at explaining the world.

Somewhat disturbingly, when the discussion of the role of science in physical therapy comes up, it is suggested that science is somehow inadequate to fully explain the questions we have.  It is often suggested that physical therapy is in one part science, but another part “art” and thus falsely argued that the imprecision and shades of gray that we encounter puts physical therapy occasionally “beyond” science.  This is a non-sequitur.  The pervasive uncertainty that we face doesn’t suggest that science is inadequate to answer our questions, it’s just merely incomplete.  There are things we don’t know, things that we don’t know that we don’t know, and what we do know is tentative.  There are certainly practical constraints we face in science, i.e. time and money, but these constraints aren’t evidence of an insufficiency with the process itself.  There is no other better way of doing what we need to do.  

Scientific Values Should Be Your Values

While science can be thought of as “a way of thinking,” it has implicit values that elevate it above other intellectual pursuits.  These values are universally useful for anyone in the healthcare field.  Let’s go through a few of these in no particular order.  

  • A commitment to metaphysical and scientific realism is embedded in one’s scientific pursuit.  Nothing about the world that we live in is in principle undiscoverable.  There is no supernatural, there are no miracles.  There are only things we have yet to understand.   
  • Intellectual humility is demanded in science.  It is extremely easy to be wrong.  As Richard Feyman has said better than I could; the first principle is that you must not fool yourself and you are the easiest person to fool.”  Scientists are quick to acknowledge that there are puzzles that we have not yet solved, but there is always someone working diligently to solve them.
  • Multiple error detection mechanisms enforce intellectual humility.  Peer review, reproducible experiments, and collective analyzation are methods to scrutinize incoming theories and reduce errors.  Scientific data is always given with an estimation of variability in order to take into account potential errors.  
  • The conclusions of science are tentative and subject to revision after error detection or the emergence of a theory that is more successful.  The knowledge we get from science is always subject to continued scrutiny.  Science acknowledges the fact that some percentage of the things we think we know are wrong, and tries to take that into account.  
  • Experimentation is the best way to truly assess the explanatory power and refutability of our theories.  The discussion of internal validity external validity, overall quality, and reproducibility warrants its own entire blog post, these are things that are essential to our scientific endeavors.
  • Falsification is a feature of good science.  When experimenting, it is made clear beforehand what constitutes success or failure of the theory, and conclusions are made accordingly.  You have to be willing to be proved wrong.  

Science is simply the broad and systematic approach to clear and rational thinking where you can actually put hypotheses to the test.  A physical therapists should be keeping these values in mind during their clinical practice.  It is vital that therapists question what they do and why they do it.  We need to be open to new theories, and know when to abandon old ones.  Perhaps most importantly, we need to consider that we may be getting fooled, and we should have an idea of what would have to happen to show that we were wrong about something.  If the answer to the question of “what would change your mind?” is nothing, then you have a problem.

Epistemological Concepts With Utility

Getting to the truth is hard.  It is easy to be deceived by your observations or fall victim to your own biases.  But those in the business of clear thinking and rational inquiry have a few tools at their disposal to enhance their scientific endeavors.  Some concepts in epistemology, or the study of knowledge, are useful for physical therapists.

One such concept, is the idea of epistemological razors, which are tools designed to simplify reasoning.  One tool is Occam’s Razor, which suggests that when given a choice between two theories, choose the simpler one.  That is, choose a theory that makes the least amount of assumptions (Sagan, 211).  This allows us to make judgments and decide which theory is better at explaining what we see.  Another such razor was popularized by author Christopher Hitchens in his book God Is Not Great: How Religion Poisons Everything.  Hitchen’s Razor posits “what can be asserted without evidence can also be dismissed without evidence” (Hitchens, 150).  The burden of proof is on the person making the claim, not with the person arguing against it.   These razors can be utilized in the following example.  How can you prove to me that there isn’t an invisible pink unicorn standing right behind you that is completely undetectable in any way?  You can’t.  The claim is completely unfalsifiable and there is no evidence for it, but using our philosophical razors, this claim can be easily dismissed as nonsense.

In addition to using razors, understanding logical fallacies can help when analyzing arguments and people’s beliefs.  Understanding these can help you detect when someone is fooling you, intentionally or unintentionally.  Let’s go through a few that are especially relevant.

  • Post hoc, ergo propter hoc refers to the fallacy of assuming that something that happened after an event was caused by that event.  There may be other confounding variables in play and a good example of this fallacy can be seen in efficacy trials for treatments.  Just because we administer a treatment to a patient and they get better, doesn’t by itself demonstrate the treatment is what actually got the patient better.  There can be other factors such as regression to the mean, placebo, nocebo, etc.
  • Strawman refers to when you argue against a version of your opponent’s argument that is easier to take down.  When debating with other professionals, it is important to “steelman” them, and argue against the strongest version of their claim.  
  • Ad hominem refers to the fallacy of attacking a person’s character or credentials instead of addressing the arguments put forth against you.  This is a way of dodging a line of reasoning and making your opponent look bad.
  • Anecdotal support refers to the fallacy of supporting your argument with your subjective experience.  This is especially relevant in the physical therapy profession; every new treatment that comes out will have its enthusiastic patients and eager practitioners.  This is simply not enough anymore to justify the efficacy of a treatment.

There are probably enough logical fallacies to warrant its own blog post, but these are just a few relevant ones.  Clear thinking is necessary to deal with the complexity that we face in physical therapy, and keeping these tools of the philosophers in mind can help.  

Dealing With The Inevitable Objections

The role of science in physical therapy is not yet a settled issue, and there is varying degrees of support for and against.  When advocating for our profession to become more science-based, you typically see objections of a few sorts, of which I will list below, and address individually.  Now these are only objections I have seen personally in interactions on social media and with discussion among colleagues.  

  • Science fails to capture the “artistic” aspect of physical therapy.
    • As mentioned above, it often argued that physical therapy is in some part “art” and has nothing to say in regards to best treatment.  It is true that we often face uncertainty and complexity in our profession that requires some “artful” decision making.  However, this is a game of probability. I admit we do not yet have all the pieces, but all science will do is increase our odds of making the right decisions.  It is difficult to imagine what a “complete science” of physical therapy would like but it seems that it is not impossible in principle.  
  • Science does not account for patient preferences or encourages us to ignore them in some cases.
    • It is often said that science cannot account for the preferences of the patient and is somehow orthogonal to them.  This is not true.  It is very clear that patient preference plays a role in the success of our interventions and overall outcome. This is something that can be assessed directly with our research by investigating patient expectations and patient satisfaction, and comparing that to patient outcomes.  
  • Science is typically done in a controlled setting to account for as many confounding variables as possible, whereas actual clinical practice is unlike the setting of an experiment.
    • Yes, science is done in a controlled setting that is in many ways dissimilar to real clinical practice.  But as mentioned above, this is a game of probabilities where we are immersed in the uncertainty associated with the clinic setting, and or job is to find the most probable solution.  There are many variables in physical therapy practice, but we need to carefully study them in a systematic way, individually.  We do not have a searchlight, only a candle.  Progress is slow because we want to be as sure as possible along each step of the way.  
  • Practitioners see results anecdotally, and science is not of much use to them. 
    • Anecdotal support for treatment is simply not enough anymore.  It is easy to succumb to cognitive biases and not realize that something else is going on.  Scientific evidence in the form of carefully controlled research is the standard in medicine now.  Unfortunately with physical therapy, we are dealing with subjective outcomes and gray areas, making it easy for something to seem effective when it really isn’t.  If you have truly seen success with your technique, put it to the test to see if it can pass the now-universal standard.  If it does, then that’s excellent and the world will be better for it.  If it doesn’t, you can start to re-focus your efforts.  The reputation of our profession is too important to be smeared by therapists dismissing the standard that everyone else in medicine uses for determining what is true.  
  • The science is often wrong or doesn’t agree with what people see.
    • Science takes this into account.  The conclusions of science are always tentative and subject to revision upon newer theories and future studies.  In science, nothing is sacred or taken as a given.  Your confidence that a theory is truly representing the way the world is ought to be proportional to the amount of evidence it has in support of it.  And that confidence is subject to continual change as new studies come out.  
  • The results of science are difficult to translate into practice, and thus has overall limited utility.
    • This is probably the most serious of contentions with bringing science to the forefront of our profession.  There are multiple barriers preventing the best evidence from being utilized in practice.  Limited time, limited experience with reading research, limited support from employers, lack of resources, and difficulty translating research into usable clinical ideas make this project difficult for many physical therapists.  Theses are all problems every physical therapist needs to consider, but theses are solvable problems.  The entire purpose of this blog is to give an honest look at what the science suggests, and convey it in an easily digestible form.  We can all deal with these issues together.   

Incorporating Scientific Thinking In Your Practice

Science is our way to illuminate the path forward for us.  We can’t just continue running into darkness at full speed.  Incorporating the values of science, the tools of the philosophers, and clear, rational thinking will be critical for us to shape our profession in the way it deserves.  Too often do we see the intrusion of profoundly unscientific ideas, unsubstantiated claims, and obvious nonsense.  Carl Sagan sums it up thusly:

“Science is a way to call the bluff of those who only pretend to knowledge.  It is a bulwark against mysticism, against superstition, against religion misapplied to where it has no business being.  If we’re true to its values, it can tell us when we’re being lied to.  It provides a mid-course correction to our mistakes…Finding the occasional straw of truth awash in a great ocean of confusion and bamboozle requires vigilance, dedication, and courage.  But if we don’t practice these tough habits of thought, we cannot hope to solve the truly serious problems that face us – and we risk becoming a nation of suckers, a world of suckers, up for grabs by the next charlatan who saunters along.”



  1. Hitchens, Christopher. (2007) god is not Great: How Religion Poisons Everything
  2. Martin, Curd. Cover, J.A. (1998) Philosophy Of Science: The Central Issues
  3. Sagan, Carl. (1996) The Demon-Haunted World: Science As A Candle In The Dark

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