[for a brief explanation of this ongoing series, as well as a full table of contents, go here]
“The wrong view of science betrays itself in the craving to be right; for it is not his possession of knowledge, of irrefutable truth, that makes the man of science, but his persistent and recklessly critical quest for truth.”
If there is one area of human endeavor where there seems to be no doubt that the concept of progress applies, that surely must be science. Indeed, more often than not, as we have seen, it is prominent scientists who hurl accusations of uselessness to philosophy precisely based on what I think is a profoundly misguided comparison between the two disciplines, where the (alleged) lack of progress in philosophy is contrasted with the (unquestioned) steady progress of science.
As we shall see in this chapter, however, it is not immediately clear exactly in what sense science makes progress, or how precisely we are to measure such progress. Not surprisingly, it is philosophers of science — together with historians and sociologists of the discipline — who have investigated some of the basic assumptions about the practice of science that (most) scientists themselves simply take for granted. And such probing has been going on since at the least the beginning of the last century, with interesting results.
Just to make things as clear as possible from the outset, I do not deny that science makes progress, in something like the way in which scientists themselves (not to mention the public at large) think it does. My goal here is to show that even so, it is surprisingly difficult to cash out an unambiguously clear picture of what this means, and to explore a number of alternative philosophical accounts of the nature of scientific knowledge. While this is not a book on the philosophy of science, and hence I will have to limit myself to only sketches of a number of complex and nuanced positions while pretty much ignoring others for the sake of brevity, it is important to go through this exercise for two reasons: first, because it should bring about some humility on the part of scientistically inclined people (or so one can hope); second, because it will put into better perspective the reasons why arguing that philosophy in turn makes progress is both not straightforward and yet perfectly plausible.
The obvious starting point: the Correspondence Theory of Truth
Every scientist I have talked to about these matters (though, of course, systematic sociological research on this would be welcome!), has implicitly endorsed what philosophers refer to as the Correspondence Theory of Truth (CToT: David 2009). This also likely captures the meaning of truth that lay people endorse, and may be at the roots of the almost universal belief that science makes progress, specifically in the sense of discovering true things about the world (or — in a somewhat more sophisticated fashion — of producing a series of theories about the nature of the world that come closer and closer to the truth). Interestingly, many philosophers up until recently have also endorsed the CToT, and have done so without even bothering to produce arguments in its favor, since it has often been taken to be self-evident. For example, Descartes (1639 / 1991, AT II 597) famously put it this way: “I have never had any doubts about truth, because it seems a notion so transcendentally clear that nobody can be ignorant of it … the word ‘truth,’ in the strict sense, denotes the conformity of thought with its object.”
Still, what, exactly, is the CToT? Here is how Aristotle put it (350 BCE, 1011b25): “To say of what is that it is not, or of what is not that it is, is false, while to say of what is that it is, and of what is not that it is not, is true.” Not exactly the most elegant rendition of it, but a concept that we find pretty much unchanged in Aquinas, Descartes, Hume, Kant and several other medieval and early modern writers. Its contemporary rendition dates to the early days of analytic philosophy, and particularly to the work of G.E. Moore and Bertrand Russell. Truth, according to the CToT, is correspondence to facts: to say that statement / theory X is true just means that there is a factual state of affairs Y in the world that is as described by X. It seems pretty straightforward and hard to dispute, and yet much 20th century philosophy of science and epistemology has done just that: dispute the CToT with the aim of carefully unpacking the notions on which it is based, and — if warranted — to replace it with a better theory of truth.
The first problem lies in the very use of the word “truth.” It seems obvious what we mean if we say that, for instance, it is true that the planet Saturn has rings in orbit around its center of gravity. But it should be equally obvious what we mean when we say things like the Pythagorean theorem is true (within the framework of Euclidean geometry). And yet the two senses of the word “truth” here are quite distinct: the first refers to the sort of truth that can be ascertained (insofar as it can) via observation or experiment; the second one refers to truth that can be arrived at by deductive mathematical proof. We can also say that the law of the excluded middle — which says that either a proposition or its negation are true, but not both — is (logically) true within the framework of classical logic. This is related to, and yet somehow distinct, from the sense in which the Pythagorean theorem is true, and of course it is even further distinct from the business about Saturn and its rings. There are yet other situations in which we can reasonably and more or less uncontroversially say that something is true. For instance, according to every ethical system that I am aware of it is true that murdering someone is wrong. More esoterically, philosophers interested in possible world semantics and other types of modal logic (Garson 2009) may also wish to say that some statement or another is “true” of all nearby possible worlds, and so on.
The bottom line is that the concept of truth is in fact heterogeneous, so that we need to be careful about which sense we employ in any specific instance. Once appreciated, this is not an obstacle unless a scientistically inclined person wants to say, for instance, that moral truths are the same kind of truths as scientific ones. As you may recall, we have in fact encountered a number of such cavalier statements already, which reinforces the point that the apparently obvious differences among the above mentioned meanings of truth do, in fact, need to be spelled out and constantly kept in mind. So, I will limit application of the CToT — within the specific context that interests us here — to empirical-scientific truths about the way the world is and works. It is of course the case that mathematicians, and even some ethicists, deploy a version of it within their respective domains of interest, but I hope it is uncontroversial that in those cases we are talking about a different type of “correspondence” (i.e., not one that can even in principle be verified by observation or experiment) — and this quite apart from my personal skepticism of mathematical Platonism (see Introduction) or of moral realism (which I will leave for another time). (For a classic, sophisticated discussion of mathematical truth taking account of the Platonist perspective see: Benacerraf, 1973.)
Even if we agree that the CToT in science makes intuitive sense if we limit ourselves to a restricted meaning of the word “fact,” we still need to examine a number of objections and alternative proposals to the theory, as they will help appreciate why to talk about progress in science is not quite as straightforward as one might think. There are several issues that have been raised about the soundness of the CToT (see David 2009 for a survey and further references), one of which is that it simply does not amount to a “theory” of any sort; in fact, it has been characterized as a trivial statement, a vacuous platitude, and so forth. This is somewhat harsh, and even if the CToT really is not anything that one might reasonably label with the lofty term of “theory” it doesn’t mean that it is either trivial or vacuous. One way to think of it is that the CToT is closer to a working definition of what truth is, particularly in science (some philosophers, like David, refer to these situations as “mini-theories”). And definitions are useful, if not necessarily explanatory, as they anchor our discussions and provide the starting point for further exploration. 
Perhaps a more serious objection to the CToT is that it relies on the much debated concept of “correspondence,” which itself needs to be unpacked (the classical reference here is Field (1972), but see also Horwich 1990). To simplify quite a bit, one of the possible answers is that defenders of the CToT can invoke the more precise (at least in mathematics) idea of isomorphism as the type of correspondence they have in mind. The problem is that — unlike in math — it is not at all straightforward to cash out what it means to say that there is an isomorphism between a scientific theory (which is formulated in the abstract language of science) and a physical state of affairs in the world. This is a good point, but as David (2009) retorts, this sort of problems holds for any type of semantic relation, not just for isomorphisms in the context of the CToT.
Another way to take the measure of the CToT is to look at some of its principal rivals, as they have been put forth during the past several decades. One such rival is a coherentist approach to truth (Young 2013), which replaces the idea of correspondence (with facts) with the idea of coherence (among propositions). This move works better, I suspect, for logic and mathematics (where internal coherence is a primary standard), but less so for scientific theories. There are simply too many possible theories about the world that are coherent and yet do not actually describe the world as it is (or as we understand it to be) — a problem known in philosophy of science as the underdetermination of theory by the data, and one that from time to time actually plagues bona fide scientific theories, as it is currently the case with string theory in physics (Smolin 2007).
A second set of alternatives to the CToT is constituted by a number of pragmatic theories of truth, put forth by philosophers like Peirce and James (see Hookway’s (2008) refinement of Peirce’s original account). Famously, these two authors differed somewhat, with James interested in a pluralist account of truth and Peirce more inclined toward a concept that works better for a realist view of science. For Peirce scientific (or, more generally, empirical) investigation converges on the truth because our imperfect sensations are constrained by the real world out there, which leads to a sufficiently robust sense of “reality” while at the same time allowing us to maintain some degree of skepticism about specific empirical findings and theoretical constructs. Here is how Peirce characterizes the process (Peirce, 1992 & 1999, vol. 1, 138):
So with all scientific research. Different minds may set out with the most antagonistic views, but the progress of investigation carries them by a force outside of themselves to one and the same conclusion. This activity of thought by which we are carried, not where we wish, but to a foreordained goal, is like the operation of destiny. No modification of the point of view taken, no selection of other facts for study, no natural bent of mind even, can enable a man to escape the predestinate opinion.
For Peirce, therefore, truth is an “opinion” that is destined to be agreed upon (eventually) by all inquirers, and the reason for this agreement is that the object of such opinion is reality. This is actually something that I think scientists and realist-inclined philosophers could live with. James’ views, by contrast, are a bit more controversial and prima facie less science friendly, for instance when he claims that truth is whatever proves to be good to believe (James 1907/1975, 42), or when he defines truth as whatever is instrumental to our goals (James 1907/1975, 34). James did qualify those statements to the effect that they are meant in the long run and on the whole (James 1907/1975, 106), thus invoking a concept of convergence toward truth that is not too dissimilar from Peirce’s. Still, by this route James arrived at his famous (and famously questionable) defense of theological beliefs: belief in God becomes “true” because “[it] yield religious comfort to a most respectable class of minds” (James 1907/1975, 40). While Hookway (2008) suggests that Bertrand Russell was a bit unfair to James when he said that the latter’s theory of truth committed him to the “truth” that Santa Claus exists, Bertie may have had a point.
There are a number of other alternatives to the CToT that need to be at the least briefly mentioned. For instance, the identity theory says that true propositions do not correspond to facts, they are facts. It is not crystal clear in what ontological sense this is the case. Then we have deflationist approaches to truth: according to the CToT, “Snow is white” is true iff it corresponds to the fact that snow is white; for a deflationist, however, “Snow is white” is true iff snow is (in fact) white. The move basically consists in dropping the “corresponds to” part of the CToT. David (2009), however, points out that many CToT statements are not so easily “deflated”; moreover, this particular debate seems to hinge on issues of semantics rather than on any “theory” of what it is for something to be true.
A position that gathers more of my sympathies is that of alethic pluralism, according to which truth is multiply realizable. As David (2009) puts is: “truth is constituted by different properties for true propositions from different domains of discourse: by correspondence to fact for true propositions from the domain of scientific or everyday discourse about physical things; by some epistemic property, such as coherence or superassertibility, for true propositions from the domain of ethical and aesthetic discourse, and maybe by still other properties for other domains of discourse.” This in a sense closes the circle, as alethic pluralism conjoins our discussion of theories of truth with my initial observation that “facts” come in a variety of flavors (empirical, mathematical, logical, ethical, etc.), with distinct flavors requiring distinct conceptions of what counts as true.
The goal of this brief overview of theories of truth was to establish two points: first, contra popular opinion (especially among scientists), it is not exactly straightforward to claim that science makes progress toward truth about the natural world, in part because the concept of “truth” itself is fraught with surprising difficulties; second, and relatedly, there are different conceptions of truth, some of which represent the best we can do to justify our intuitive sense that science does indeed make progress in the teleonomic sense of approaching truth, and others that may constitute a better basis to judge progress (understood in a different fashion, along the lines of our discussion in the Introduction) in other fields — such as mathematics, logic, and of course, philosophy.
 It should be obvious that truth as understood here is a property of propositions and statements, but not of other things. “The truth,” then, is not a concrete entity to be found, nor is it an abstract object apart from the class of true propositions.
Aristotle (350 BCE) Metaphysics (translated by W.D. Ross) (accessed on 31 May 2013).
Benacerraf, P. (1973) Mathematical truth. The Journal of Philosophy 70:661-679.
David, M. (2009) The Correspondence Theory of Truth. Stanford Encyclopedia of Philosophy (accessed on 8 May 2013).
Descartes, R. (1639 / 1991) Letter to Mersenne: 16 October 1639. In: The Philosophical Writings of Descartes, Vol. 3. Cambridge University Press.
Field, H. (1972) Tarski’s theory of truth. The Journal of Philosophy 69:347-375.
Garson, J. (2009) Modal Logic. Stanford Encyclopedia of Philosophy (accessed on 31 May 2013).
Hookway, C. (2008) Pragmatism. Stanford Encyclopedia of Philosophy (accessed on 4 June 2013).
Horwich, P. (1990) Truth. Blackwell.
James, W. (1907 / 1975) Pragmatism: A New Name for some Old Ways of Thinking. Harvard University Press.
Peirce, C.S. 1992 and 1999. The Essential Peirce. Indiana University Press.
Smolin, L. (2007) The Trouble With Physics: The Rise of String Theory, The Fall of a Science, and What Comes Next. Mariner Books.
Young, J.O. (2013) The coherence theory of truth. Stanford Encyclopedia of Philosophy (accessed on 4 June 2013).