A near verbatim transcript of the talk I gave on September 26, 2025, at RatFest in Philadelphia.
I’m going to talk about the correspondence theory of truth.
For those who don’t know what that is, it’s the idea that a true theory is one that “corresponds to the facts”, and that the growth of knowledge consists of making our theories correspond better and better to the facts over time.
Now, I think most critical rationalists accept this theory. Both Karl Popper and David Deutsch have attempted to connect it explicitly to critical rationalism, Popper with his theory of “verisimilitude” and Deutsch with his theory of perfectly true abstract propositions.
But I want to criticize the correspondence theory of truth from the point of view of critical rationalism, because critical rationalism tells us to judge theories by their explanatory power, and I’m going to argue that the correspondence theory of truth plays no role in the explanatory power of critical rationalism.
So, to lay out this argument, I first need to summarize critical rationalism as I understand it. Critical rationalism is a theory of knowledge, of course, and it explains the growth of knowledge as a process of evolution. This isn’t some kind of analogy to biological evolution. It’s saying that the growth of knowledge in a mind is literally a form of evolution unto itself.
Popper liked to summarize the theory using this four-step schema:
Problem → Tentative Theories → Error Elimination → New Problems
We start with a problem. We guess tentative theories to solve it. We subject those theories to a process of error elimination by criticizing them. Then, should we find that one of our theories solves our problem and survives all our criticisms, that theory gives rise to a new generation of problems that can be solved in turn, by the same process.
According to this theory, the mind is a kind of ferment of creativity, with ideas constantly coevolving with each other, accumulating further and further adaptations to solve deeper and deeper problems, rendering each particular mind utterly unique.
Now, I just gave a high-level summary of critical rationalism, and you’ll notice that nowhere in that summary did I mention the correspondence theory of truth. And in a way, that’s my whole argument.
But you often do hear critical rationalists mention it, usually as a kind of appendage to the main body of the theory I just described. They’ll give a summary like the one I just gave, and then they’ll append to it a further statement, something like, “…and by this process we get closer and closer to the truth,” and by “truth” they mean “correspondence to the facts”.
But if the coin of the realm is explanatory power, I don’t think we can be satisfied with the correspondence theory of truth as an appendage to the main body of critical rationalism. I think we need to ask ourselves whether correspondence can be integrated explicitly into Popper’s schema.
Now, I don’t think I’ve ever seen a critical rationalist attempt to argue that we can use “correspondence to the facts” as an actual criterion for generating or selecting theories. And that’s not surprising, because in the correspondence theory of truth, the phrase “the facts” means something like “perfect metaphysical truths about reality”, or perhaps “things in themselves”, but according to critical rationalism, we can never have “the facts” in that sense. So I think from the point of view of critical rationalism, it’s pretty clear that we couldn’t possibly consult “the facts” to generate true theories. And for the same reason, we couldn’t possibly apply “the facts” as a criticism to eliminate false theories, because that would just be another way of consulting “the facts” to generate true theories.
But critical rationalists do sometimes try to incorporate correspondence into Popper’s schema in a more subtle way, and that’s through a very specific interpretation of the phrase “error elimination”. The argument goes something like this: “Although we can never reach the truth, we can eliminate errors. The existence of error implies the existence of truth. And the possibility of eliminating errors implies the possibility of obtaining some of this truth in our theories.”
There’s a big problem with this argument from the point of view of critical rationalism. Specifically, it takes the word “error” to mean something like “metaphysical falsehood”. But remember, critical rationalism is a theory of evolution. And in the context of a theory of evolution, “error” doesn’t mean “metaphysical falsehood”.
In the context of a theory of evolution, “error” means maladaptation.
So, when we talk about “error elimination” in critical rationalism, we’re not talking about purging metaphysical falsehoods from our theories. We’re talking about fixing theories that are maladapted to their problem situations so that they become better adapted to their problem situations. Correspondence simply doesn’t come into it.
Now in my mind, this is all good news, because there are all these criticisms out there of the correspondence theory of truth, and if critical rationalism invokes correspondence, then we have to address those criticisms. And that’s what verisimilitude and perfectly true abstract propositions are—they’re attempts to address some of those criticisms. But if critical rationalism doesn’t invoke correspondence, then those criticisms have no implications for the theory.
Plus, we can retain critical rationalism’s full explanatory power without the extra baggage of verisimilitude or perfectly true abstract propositions. And by dropping all that extra baggage, we make critical rationalism harder to vary.
Some of you may be thinking there’s bad news here as well, though, because my argument that we should drop the correspondence theory of truth may seem like an argument for dropping the concept of truth altogether. But that’s actually not the case, and this is the point I want to end on.
I think the concept of truth does play a very important role in critical rationalism. Popper often wrote of the importance of the critical attitude in driving the evolution of our knowledge. And I think adopting a critical attitude toward our theories is essentially the same thing as being interested in the truth. And without that, we’d be doomed to wallow in our maladapted ideas until eventually they killed us all.
I think critical rationalists hold on to the correspondence theory of truth because they want to defend the idea that the growth of knowledge is about the search for truth. And I want to defend that idea as well. But I don’t think we need the correspondence theory of truth, or any other “theory of truth” in that sense, to be interested in the truth, and for that interest in the truth to inspire in us a critical attitude toward our theories, and for that attitude to drive the evolution of our knowledge into deeper and deeper realms of inquiry, forever and ever, without limit.
Addendum: In follow-up conversations, Dennis Hackethal raised an interesting counterargument not addressed in my talk. He posed the question of whether the universality of computation doesn’t imply some form of correspondence. If, according to the theory of computation, it’s possible to build a universal computer that can simulate all possible motions of all possible objects, do we not need some notion of correspondence to express that fact? In other words, do the simulated objects and motions not in some sense necessarily “correspond” to the objectively real, physical objects and motions that they simulate? And is scientific thinking not merely a special case of such simulations?
I’m still thinking through that argument, but I suspect the relationship between the simulation and the “things” simulated can be expressed in terms of the “self-similarity” property of physical reality rather than in terms of “objects and their motions”. And I suspect that it’s the latter formulation, specifically because it invokes “objects”, that seems to imply the need for some form of correspondence.
I’m certainly a realist, although I think any attempt to describe reality “in general” or “as a whole” must in some sense be doomed to fail, given the necessarily partial and conjectural nature of knowledge. Still, I can’t conceive of how objective physical reality, whatever it is and whatever its character, could be inherently parsed into objects. In other words, it seems unavoidable to me to think of physical reality as a single object.
In that framing, we can express the universality of computation without reference to “objects and their motions”, referring instead to a special property—self-similarity—that characterizes the object “as a whole”. The simulations running inside a universal computer, and the actual physical processes being simulated, might be understood as identical configurations (or structures) of information that are scale invariant, meaning the information structure is completely identical, despite the fact that one instantiation of it might be much larger than the other (e.g., two black holes colliding vs. a simulation of that collision in a computer). In fact, the computer itself need not be thought of as “an object” either. It can be thought of as an information structure as well, just like the colliding black holes—a mere aspect of the unfathomably huge object we call physical reality. 1
Also, in separate conversations with Dennis and with Erik Orrje, I raised another argument against correspondence that may be decisive even if we assume that physical reality is parsed inherently into objects. Namely, if the evolution of knowledge in each particular mind renders that mind utterly unique, then no two versions of a given concept (e.g., “the planet Jupiter”) can possibly be identical across multiple minds. Which is to say that the version of that concept in any one mind will necessarily be enmeshed in and affected by a vast structure of evolved meanings and associations that are idiosyncratic to that mind’s evolutionary history. So, if we imagine ourselves to be making statements that “correspond to the facts”—for example, “Jupiter is 817 million miles from the sun at its aphelion”—we’re forced to ask: Whose idiosyncratic version of the concept “Jupiter” corresponds to the actual planet?
- For a discussion of the universality of computation in terms of the “self-similarity” property, see Deutsch’s book, The Fabric of Reality, 1997. ↩︎