The physicist P.W. Bridgman wrote extensively on the philosophy of science and is best known for his wide-ranging defense of the “operational method” as a means of getting clear on what we mean by our use of scientific concepts. He is also well-known for the controversial claim that science is essentially a private affair.
Such a claim strikes most of us as odd, but Bridgman claims this is a result of socialization, not reality. We are brought up to think that science is ultimately a public affair, a matter of bringing all knowledge into the public domain, making our research transparent and replicable, our methods visible to all, our facts public, etc. Moreover, in the age of “Big Science” where collaboration between huge teams of people is the new norm in science, the individual component of science is downplayed in favor of consensus, team-building, and the public nature of knowledge.
Bridgman disagreed fundamentally with this view. Instead, Bridgman thought of science as an essentially private affair of individual human scientists struggling to understand the world around them. Why? Bridgman placed a lot of emphasis on the importance of operations in science such as the operation of measuring or double-checking a measurement. Moreover, Bridgman thought that operations are private in the sense that operations are carried out by individual scientists.
Anticipating recent developments in the philosophy of peer disagreement, Bridgman asks us to imagine that you have calculated a mathematical problem and arrived at the answer of 173. Suppose your neighbor says, “Oh, you’ve got that all wrong, the actual answer is 170.” Bridgman asks, would we just take this on testimony? Hardly! If we blindly accepted our neighbor’s answer we would be poor scientists. Rather, what a good scientist would do is double-check the methods used by the neighbor and investigate whether they are performing the same mathematical operations in the same way as we are. Any divergence in the answer must be due to a divergence in operational methods and resolution of the issue will only occur if we cross-check our methods. Not until we have verified the operations ourselves and arrived at the correct answer can we say we have really “understood” the problem. And this is the crux of the issue: understanding.
Bridgman uses peer disagreement as an analogy for all of science. The goal of all scientists should not be consensus without personal understanding, but personal understanding of the consensus. Thus, Bridgman thought that there are as many sciences as there are scientists, with the goal of every scientist being the goal of understanding the world around them. As Sam Harris puts it, “The core of science is not controlled experiment or mathematical modeling; it is intellectual honesty.” Or, as Bridgman famously said, “The scientific method, insofar as it is a method, is doing one’s damndest with one’s mind, no holds barred.”
Why did Bridgman care about the privacy of science so much? It’s because he thought that his peers had not sufficiently appreciated the distinction between the “private level of meanings” and the “public level of meanings”. For example, take the imperative “Verify whether X is 10 meters long.” This imperative can be fulfilled by any scientist so long as they use the conventional operational methods e.g. a meter-stick. Nothing private about that. Now, in contrast, take the imperative “Verify whether X has a toothache.” Crucially, the methods used to carry out this imperative vary drastically depending on who the X is. If the X refers to myself, I can hardly communicate how it is that I “know” I have a toothache. I just introspect it “directly”. In contrast, if the X refers to my neighbor, the method of verification is going to be extremely indirect. It becomes even more difficult when the X refers to a non-verbal animal, like cat or rat.
Bridgman took this all as incontrovertible evidence that psychologistic terms have a “dual meaning”. The concept of a “toothache” has both a private and a public meaning according to the method of operationalism. The private level is due to the fact that the method I use to verify my own toothache is very different from how I verify if anyone else has a toothache. But the public level comes from the fact that everyone understands what I mean when I say “My toothache”. They are understanding the public level. On the public level we are allowed to say “My neighbor’s toothache” even though the methods of verification are radically different. But when you examine the issue carefully, there are really two concepts at work: “Toothaches-for-me” and “Toothaches-for-you”.
Bridgman thought this duality of meaning is rampant but not well-appreciated. Once we realize that there are some operations that are essentially private, we come to the realization that, as Bridgman says, “We can never get away from ourselves.” Even science, the most “public” of all activities, is going to have some concepts that have the private/public duality. This is particularly true for psychological sciences, where the problem of operationalism is most striking. When a psychologist studies “consciousness”, the methods of study will look drastically different depending on whether they are studying themselves, other humans, or non-human animals. “Introspectional” words like “consciousness” or “pain” have a private nature, but scientists must study them in other creatures using only the public-level of meaning.
The mistake though is to completely ignore the private level and act like everything has been accounted for if we have the complete account in behavioral terms. However, this is not to say that Bridgman endorses dualism, or that a recognition of the private level of meaning is due to the fact that physicalism is false. As Bridgman notes, the privacy of meanings can be explained by the fact that my brain is in my skull and your brain is in your skull. If we were born with fused brains, or a clever neuroscientists managed to splice us together, the “essential” privacy of introspectional terms would lose some of essentialness. Thus, privacy is a contingent fact about organisms, not a fundamental fact of how the universe works.
But nevertheless, privacy of introspectional terminology is a fact of life that everyone must eventually come to grips with. One worry is that the emphasis of privacy leads to a kind of solipsism where we are alone in the universe of our own minds. But so what? Maybe this is true. So long as solipsism is not taken to be the view that only my mind exists, the thesis of solipsism has an element of truth if it is stated only in terms of privacy, not existence.
I can be perfectly happy claiming that other minds exist, but I must resolve myself to the fact that the method of verifying other minds feel pain in the way I do is essentially different from the way I verify my own feelings of pain. And the same applies to every other kind of mental phenomena, including perceptions, feelings, meanings, etc. The method I use to determine if you perceive the same thing as I do is different from the method I use to determine what I perceive. The method I use to know what I mean by a certain word is essentially different from the method I use to know what anyone else means by the term, and I can never be sure we mean exactly the same thing unless there is agreement about operational methods. But as we have seen, some operations are essentially private and we must learn to live with that.