How pragmatism resolved the age old battle between rationalism and empiricism (or what is the scientific method?)

If you want to simplify philosophy of science down to the point of gross oversimplification, it has been a millenia long debate between rationalism and empiricism. Although both could be found among the classic Greeks, rationalism was dominate from the time of the Greeks to the Renaissance (almost 2000 years). Rationalism holds that knowledge comes from logical thought. Think Euclid who established the axioms/proofs style of geometry. Or Plato’s cave which emphasized that our senses are crude and misleading (observing mere shadows on the cave wall) in capturing the underlying true essence (the perfect objects outside the cave creating the shadows which we cannot see). Empiricism on the other hand believes that knowledge comes from our sensory experiences of the world outside our mind and mistrusts the mind. Empiricism and rationalism are endpoints of epistemology (the philosophy of how we know things). But they have also been major motivators for scientists framing how to do science.

Leaving behind the stunted middle ages which froze into permanence the Greek views of rationalism, Galileo is an interesting transition figure. He presented his work in a series of books over the first few decades of the 1600s by having two characters argue with each and present rational arguments. This is rationalist. But what he actually did was carefully measure falling bodies, time them, and describe a mathematical pattern. And observe four moons orbiting Jupiter with a telescope. Which are both empirical. Newton too stands at this transition point. His Principia in 1687 is presented entirely in a theorem/proof format (Euclidean inspired rationalism). But what he did was provide a theory which simultaneously described Galileo’s empirical finding and Brahe’s painstakingly measured movements of planets captured in a mathematical pattern by Kepler. Again a rationalist sheen on a deeply empirical work. Coming in between Galileo and Newton was Francis Bacon whose book Novum Organum (1620) was a philosophical argument for empiricism. Bacon was nearly the first (certainly the most prominent ) person in ~2000 years in the Western world to take on the rationalist view that the Greeks had left modern science. He made a powerful and explicit argument for empiricism as a superior approach. Bacon emphasized the ability of our minds to fool ourselves and turned to empiricism as a superior alternative: “The syllogism is made up of propositions, propositions of words, and words are markers of notions. Thus if the notions themselves (and this is the heart of the matter) are confused, and recklessly abstracted from things, nothing built on them is sound. The only hope therefore lies in true Induction.”

The fight was on. The next few centuries can be fairly described as an epic battle between empiricism and rationalism. In each generation there were partisans for both empiricism and rationalism. Hobbs, Berkeley, Hume & Locke argued forcefully for empiricism. Descartes (with his clockwork universe), Leibniz and Spinoza argued for rationalism. Obviously this fight did not seem to particular distract or slow down scientists given the the development of much of the basics of chemistry, biology, physics and earth sciences in this period. Scientists seemed to just do what worked and thus seemed in some ways removed from the philosophical debate that had been ignited.

But circa 1900 two Americans, Charles Pierce (a diverse scientist and pronounced like Persh Purse) and William James (a  psychologist) developed the theory of pragmatism. I don’t think it is a coincidence that they both practiced science. Pragmatism returned to Aristotle’s modes of logic known as induction and deduction, and they added in a third point, abduction (which also has roots in Aristotle but is much more developed by Pierce and James. These three modes can be distinguished in how they relate two propositions, A and B. Namely:

  • Deduction says if A is true then B must be true. A necessarily implies B. This has very clear ties to the axiom/proof view of Euclid and to rationalism.
  • Induction says if A is true then B is likely true. Induction is fundamentally different than deduction in being a probabilistic claim rather than an absolute claim. In practice it also often differs from deduction in that A is an observation instead of an assumption.  It sometimes can involve notions of generalization. Thus the famous example of if I have observed 100 swans and they are all white, then I induce that all swans are white (but recognize that is not a certain claim as indeed the next swan could be black). But this swan example is a rather narrow view of induction – I prefer a view emphasizing observation and probability as a more useful definition than the narrower notion of generalization.*
  • Abduction says having observed B, A is a likely explanation for B.

Now we can apply these three terms to the scientific method. It is interesting that there is not one canonical version. To me this is just evidence that there is no such thing as a single cook book recipe of the scientific method. But one version puts induction in the front. We observe patterns and induce a hypothesis. From the hypothesis we deduce a prediction. And then we test the prediction. Others start from a hypothesis, deduce a prediction, and then use induction to test the hypothesis (note that this implies the test is a probabilistic outcome rather than an absolute decision on the truth of the hypothesis). Note that in both cases the hypothesis leads to prediction by deduction. That is the one universal.

But what Pierce and James did was much more subtle and useful. You know how in every major debate in ecology, the answer is “both”. Top down vs bottom up? Both. Density dependence or environmental control? Both. And etc. This is basically what Pierce and James did. They said science is a fruitful blend of induction, deduction and abduction chasing and following after each other. So instead of debating empiricism vs rationalism, they said both and lets add in abduction.

I like both halves of this elegant approach. The “both” answer for empiricism vs rationalism is so obviously right (but less fun for philosophers to argue over). But I really love the notion of abduction. Abduction is the first real attempt by philosophers to describe where hypotheses come from. This is the thing that has always bugged me the most about elementary school teachings of the scientific method. It always starts with “step 1 – come up with a hypothesis” with no comment about where it comes from. In my experience this leaves many people with the impression a hypothesis can be any old guess or arbitrary claim. Which is not at all how science works. Pierce especially brought in abduction as having a notion of likeliness mixed with explanation. Not all hypotheses are equal. Scientists are only looking for likely hypotheses. Which is of course how science really works. We don’t pick any old hypothesis. We try hard to come up with likely hypotheses explaining our observations and then proceed to test. I cannot stress enough how important I think it is to have a philosophical study of the question of where scientific hypotheses come from. There has been little additional development of abduction since Pierce and James. Which means it is still poorly understood even though all of us do it and it is central to science.

And to me pragmatism is the best and most accurate description we have of science and the scientific method. Provide a healthy mix of induction (pattern finding from the empirical world), deduction (logic which includes but is not exclusive to mathematical theory), and abduction (finding likely explanations). Throw in skepticism (which Bacon also argued for). And that is pretty much it. The scientific method is not a four step process. It is an artful concoction of four ingredients: induction (=empiricism*), deduction (=rationalism), abduction and skepticism. (I have a vision of a master chef carefully choosing the mix of ingredients to create a specific desert). Now THAT Is something I could get behind teaching as a scientific method.

So what do you think? Have I oversimplified to the point of doing violence to these ideas? Do you like the notion of abduction. Where exactly do your hypotheses come from? Do you like the notion of science and the scientific method as a blend of four modes of thinking (induction, abduction, deduction, and skepticism).


*NB – there are two senses of the word induction. Some use it in a narrow sense as numerical generalization (as in the swan example) which is closely related to the idea of proof by induction in math. This is clearly a narrower concept than empiricism. But if you take the broad sense as “facts or observations that imply the likelihood of some other observation” then it is not much of a stretch to equate it to empiricism. Especially if you start to dwell on how you get from sensory inputs to knowledge. At some point you have to start to convert those sensory inputs into statements about the likelihood of things more general than those inputs (otherwise you could never have knowledge been the current moment). And modern philosophers of science from Popper to Lakatos have emphasized that a single experiment is not decisive about the hypothesis it tests but on a certain level only changes our sense of the likelihood of that hypothesis. In this sensu latu usage it is very fair to equate induction and empiricism (and the word induction was used in the quote above from Bacon as central to what he was arguing for).



17 thoughts on “How pragmatism resolved the age old battle between rationalism and empiricism (or what is the scientific method?)

  1. I found this extremely well stated and agree that we could use more explicit recognition that “both” is perhaps the best approach. It would be interesting to know if you could actually equate “scientific progress” (however that might be measured…) with the relative mix of theoretical vs empirical (or deductive vs inductive – noting that those aren’t exactly the same thing, but similar) approaches being employed.

    This also brought to mind this piece that I think is making a similar case:
    You can’t build edifices without bricks, but bricks left in piles are equally insufficient…

    • Certainly the landmark launches of modern science that I mentioned (Galileo & Newton) not only were a mix of “both”, they were landmarks because they were a mix of “both” and reintroduced that view of science to the Enlightment. I don’t know if you could draw a direct line between the mix and progress but it would be fun to see somebody try.

      That was a fun link. I think you could probably write a matching one about “builders” who didn’t care if their bricks were real or made of air (to my read it made more fun of the empiricists than the rationalists). Both the empiricists and rationalists go off the rails without the other.

      • Yes agreed – there was also some unnecessary shade thrown at “junior scientists” in there…

      • Forscher was clearly calling for a new type of builder or or perhaps a landscape architect who could survey the vast inventories in brickyards, and with some fancy organizational analysis, produce some meta-buildings…

  2. Gary Mittelbach and you have a book out soon ….on Community Ecology. In a great video talk available on line, which I cant find now, Gary reviews the history of community ecology, and ends with a graph/diagram from the book where you 2 lay out the possible influences on community structure, and suggest that understanding on communities really consists of knowing what/where/how-often specific possibilities are realized in nature. This is also the theme of Vellend’s community structure book.

    Perhaps you could use this example to illustrate the process you describe above.

    Which is how most theorists[actually, most good scientists I know], if not philosophers, go about actually doing science. Which is why some of us pay little attention to philosophy of science.

    • Yes Gary has a very nice perspective made very clear in the first edition (unfortunately lost a bit in the 2nd edition) of proceeding from theory to experimental test to evaluation of its generality/importance in the real world.

      I think the criticism of philosophy of science as irrelevant to practicing science is a fair one; one which some philosophers of science are now worrying about.

      But I also worry if practicing scientists proceed only on intuition and unspoken assumptions. Whether the language comes from philosophy or not, I think it is important for scientists to be explicit about and be able to actively discuss and explain their methods.

      • I think many scientists are quite able to be explicit and discuss their methods; and teach them to the next generation. They just don’t source them to philosophers of science.
        I realize my position is not fashionable, and also believe that some scientists I really respect seem to have gotten positive benefits from reading philosophy of science. I certainly tried in my early days; but it was a bust.

        For an overview of this ‘against philosophy’ perspective, I recommend chpt 7 in steven weinbergs’s 1993 book… DREAMS OF A FINAL THEORY;…. ‘against philosophy ‘ is the chapter title.

        To be a foraging theorist, given the possible uses of one’s time and the set of possible intellectual morsels , philosophy of science is not in my optimal set.

      • Greeks and Romans may be celebrated for their philosophy, but their practical engineering knowledge was AMAZING. The built aquaducts, roads, and so much more. I have long been surprised how little of this is taught as part of history/philosophy of science.
        A very fine introduction is here:

        And as of todays date [ march 13/2019] the video class is on sale for little cash.

  3. You should avoid using “likely” to describe Peirce’s idea of abduction because it suggests an association with likelihoods and probability which is confusing.

    Abducting a hypothesis shows that the hypothesis may be and that it is worthy of pursuit. It does not show any probability that the hypothesis is true, it does not supply evidence. Evidence for a hypothesis comes from Induction.

    This is important because later philosophers conflate Abduction with Inference to the Best Explanation as a rule of inference. IBE tells you to infer that the best explanation of a phenomenon is true. They should be kept distinct.

    A good slogan comes from Peirce’s sixth Harvard Lecture:
    “Deduction proves that something must be, Induction shows that something actually is operative, Abduction merely suggests that something may be.”

    • I agree with most of your points, although I read Pierce as saying something stronger than abduction comes up with something “worthy of pursuit” – while I agree it is not a statement of likely truth, it is a notion that it is near the top of the list of the infinite set of possible hypotheses.

  4. Pingback: How pragmatism resolved the age old battle between rationalism and empiricism (or what is the scientific method?) — Dynamic Ecology | Hacia una Cultura Científica

  5. Brian I’ve only read about Pierce, in particular Deborah Mayo’s commentary on his thought. If I wanted to read Pierce, what would you recommend? I ask bc Pierce wrote a lot of stuff, and it’s never been collected AFAIK.

    • The book “Philosophical Writings of Pierce” is a nice collection of some his key (and accessible works). It is a Dover Press book so cheap as well.

      You can also find his article “”Deduction, Induction, and Hypothesis” published in Popular Science Monthly easily available on the internet (he had a series of publications in this magazine).

  6. Since you mentioned Descartes, here’s a joke. René Descartes walks in to a bar. The bartender asks, “Would you like a beer?” Descartes says, “I think not.”, and disappears.

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