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Philosophy of Science 101: Scientific Realism


The Philosophy of Science series explores both general questions about the nature of science and specific foundational issues related to the individual sciences. When applied to such subject areas, philosophy is particularly good at illuminating our general understanding of the sciences. This 101 series will investigate what kinds of serious—often unanswered—questions a philosophical approach to science exposes through its heuristic lens. This series, more specifically, will look at the ‘Scientific Realism’ debate throughout, which questions the very content of our best scientific theories and models.

Philosophy of Science 101 will be divided into the following chapters of content:

2. Philosophy of Science 101: Scientific Realism

3. Philosophy of Science 101: Anti-Realism

4. Philosophy of Science 101: Realism and Anti-Realism ‘Compromise’

5. Philosophy of Science 101: Causation

6. Philosophy of Science 101: Scientific Models

7. Philosophy of Science 101: Models of Explanation

8. Philosophy of Science 101: Laws of Nature

9. Philosophy of Science 101: Science and Social Context

Philosophy of Science 101: Scientific Realism

Philosophical thinking can contribute a great deal to the advancement of science at all levels of the scientific enterprise from theory to experiment, as discussed in the first article of this series. The philosophy of science explores scientific theories and "knowledge" in great depth, noting the ampliative nature of such theories which go far beyond what human beings can directly observe. This is the scientific realism debate, the very focus of this article and subsequent articlesstarting with the realist stance.

Debates around scientific realism are closely connected to almost everything else in the philosophy of science as they concern the nature of scientific knowledge. Hence the scientific realism debate is hereafter considered throughout this series, including variants of both realism and anti-realism, common arguments for and against each position, and the most important counterparts to each position. This article introduces the debate and considers one side of the story: scientific realism. In particular, this article explores the famous "no miracles" argument in favour of scientific realism.

Figure 1: Martin Luther in the Circle of Reformers, 1625–50 (oil on panel). This age fostered a "new" science relying on experiments/empirical information (Wootton, 2017).

The Debate

Empiricism is an epistemological theory in philosophy holding that knowledge or justification comes only or primarily from sensory experience. It is one of several views within epistemology and proves crucial in scientific method. Empiricism in the philosophy of science, for example, emphasises empirical evidence—especially discovered via experiments—as a fundamental part of the scientific method to produce knowledge. All hypotheses and theories must be tested against observations of the natural world rather than resting solely on a priori assumptions (knowledge which proceeds from theoretical deduction rather than from experience or observation). Empirical observation undeniably plays an essential role in science, yet the debate on scientific realism results from a tension between the empiricist methodology and claims to the effect that science can unveil the fundamental nature of reality (Ruyant, 2021). Broadly speaking, are "successful" scientific theories concerning unobservable entities and processes justified? (Shand & Bird, 2003). Should one believe what science postulates and proposes beyond the appearances of things? Realists and anti-realists propose different ways of answering such questions and of interpreting science as a whole. More particularly, realists and anti-realists propose different ways of interpreting possible scientific achievements, scientific aims, and scientific theories’ content (Ruyant, 2021).

Scientific realism, on the one hand, is a positive epistemic attitude toward the content of the best theories and models, recommending belief in both observable and unobservable aspects of the world described by the sciences. The distinction here between the observable and unobservable reflects human sensory capabilities: whereas the observable may be perceived by the unaided senses under favourable conditions (for instance, planets), the unobservable is that which cannot be detected this way (such as proteins and protons). This indeed differs from some scientific conceptions of observability which generally extend to things that are detectable via instruments (Shapere, 1982). The distinction itself has been problematised by some and defended by others. If it is problematic, this is arguably only a concern for certain forms of antirealism which adopt an epistemically positive attitude only with respect to the observable (unlike scientific realism which ultimately does not epistemically discriminate between observables and unobservables).

Figure 2: In 1981, researchers Gerd Binnig and Heinrich Rohrer invented the scanning tunnelling microscope which can now image individual atoms (Binnig, 2006).

As Stathis Psillos (1999) puts it, realism about science “is the view that mature and genuinely successful scientific theories should be accepted as nearly true” (p. 162). Scientific realism is thus a commitment to the idea that our best theories have a certain epistemic status: they yield knowledge of aspects of the world, including unobservable aspects. This position then incorporates three different stances (Psillos, 1999): first, the world has a mind-independent structure. On this metaphysical stance, objects indeed continue to exist even when there is no one there to see them. This is to say that reality is prior to thought, and humans may discover features of the world that are there independently of any observer.

Second, scientific theories according to the semantic stance are capable of being true or false. "Semantic" realism in this sense concerns the content of scientific theories. Theoretical assertions (often referring to unobservable phenomena) as such may not be reduced to claims about the behaviour of observable phenomena. Further, theoretical assertions are not merely instrumental devices for establishing connections between observables. Instead, theoretical terms in scientific theories have putative factual reference. Scientific theories may provide literal descriptions of their subject matter and can be true or false. Hence if scientific theories are true, the unobservable entities they posit populate the worldtheoretical terms made by the theory refer to the entities they postulate. Thirdly and finally, there is what is called the epistemic stance of scientific realism, relating to the possible achievements of science. Scientific realism regards successful scientific theories as well confirmed and approximately true of the world on this stance. Importantly, the entities posited by such theories do inhabit the world according to the epistemic stance.

Figure 3: Dalí's "Galatea of the Spheres" [1952]: the outcome of a Dalí impassioned by the theories of the disintegration of the atom (2014).

Each dimension of scientific realism—metaphysical, semantic, and epistemic—may progressively defend itself against varying "levels2 of the rival epistemologies of science (known collectively as forms of antirealism) in the debate over the use of unobservable entities and mechanisms (Psillos, 1999) by scientific theories to describe phenomena that is observable. Antirealism opposes realism and notably encompasses many varieties contesting each realist stance named above. Antirealism might reject the metaphysical stance, for example, denying that the world is mind independent. Various antirealist variants will be explored in the next episode of this series.

In sum, one must ask why scientific theories should be taken as "true" in the debate around scientific realism. More specifically, one must ask why there can be any belief that the entities posited by the "best" scientific theories are real. The debate, in sum, concerns the capability of supposedly successful scientific theories to truly describe the world. As mentioned, this article is exploring realism specifically. Philosopher of science Hilary Putnam’s (1975) prominent "no miracles" argument for realism is therefore especially notable.

Figure 4: Photograph of the late Hilary Putnam, responsible for the "no miracles" argument (Marquard, 2016).

No Miracles Argument

The "no miracles" argument is arguably the most influential argument in favour of scientific realism (Dawid & Hartmann, 2018), suggesting that scientific realism can provide an explanation of the success of science. Putnam (1975) argues that science often gets things right, and so the argument begins with the widely accepted premise that the best scientific theories are extraordinarily successful since they facilitate empirical predictions, retrodictions, and explanations of the subject matters of scientific investigation, often marked by astounding accuracy and intricate causal manipulations of the relevant phenomena. What then explains this success? An explanation favoured by scientific realists is that the best theories are in fact (nearly) true (they correctly describe a mind-independent world). Indeed, miracles do not exist according to Putnam’s (1975) argument. If successful theories were far from the truth, so the argument goes, the fact that they are vastly successful would be entirely miraculous since the "best" scientific theories give true or approximately true descriptions of observable and unobservable aspects of a mind-independent world according to realism.

Notably, "truth" is approximate truth generated by the very best (widely accepted) scientific theories or aspects thereof. The realist motivation for this is as follows. If one is to defend a positive epistemic attitude regarding scientific theories, it is presumably sensible to do so not merely in connection with any theory (especially when one considers that, over the long history of the sciences up to the present, some theories were not or are not especially successful), but rather with respect to theories (or aspects of theories), that would appear, prima facie, to merit such a defence. These are namely the best theories (or their aspects). It is widely held, not least by realists, that even many of the best scientific theories are strictly speaking likely to be false. Hence the importance of the notion that theories may be close to the truth (that is, approximately true) even though they are false (Chakravartty, 2017). The challenge of making these qualifications more precise, however, is significant, and has generated much discussion: unfortunately beyond the scope of this article. Most importantly, according to Putnam's (1975) argument, one should always favour the so-called "non-miraculous" explanation that scientific theories are successful since they correctly describe the worldthis is not a miracle, it is instead because they are true or approximately true as reflected by their success (Chakravartty, 2017).

Figure 5: Philosopher of Science Thomas Samuel Kuhn (1922–1996), famous for his theory of scientific revolutions (Day, 2022).

This may be supported by "inference to the best explanation" ("IBE") and naturalism. The model of IBE is often used in science and is designed to give a partial account of many inductive inferences. One version of the model was developed under the name "abduction" by Charles Sanders Peirce early in this century, and the model has been considerably developed and discussed over the last 25 years (Lipton, 2017). Its governing idea is that explanatory considerations are a guide to inference (i.e., a conclusion reached on the basis of evidence and reasoning), that scientists infer from the available evidence to the hypothesis which would, if correct, best explain that evidence. Of course, many inferences are naturally described in this way. Charles Darwin, for instance, inferred the hypothesis of natural selection because, although it was not entailed by his biological evidence, natural selection would provide the best explanation of that evidence (Lipton, 2017). Likewise, when an astronomer infers that a star is receding from the earth with a specified velocity, they do this because the recession would be the best explanation of the observed red-shift of the star’s characteristic spectrum.

IBE can therefore be seen as an extension of the idea of "self-evidencing" explanations, where the phenomenon that is explained in turn provides an essential part of the reason for believing the explanation is correct. Self-evidencing explanations admittedly exhibit curious circularity, but this circularity proves benign and is in fact a common situation in science, for hypotheses are often supported by the very observations they are supposed to explain. In the context of Putnam’s (1975) argument for scientific realism, it is realism that proves better than any other philosophical position to explain the success of science. As mentioned, naturalism is also part of this IBE-based argument. According to naturalism, one must appeal to explanatory power, simplicity, strength, and comprehensiveness: all of which scientific realism provides on Putnam’s (1975) account and as an explanation for the success of scientific theories.

Figure 6: Philosophy professor Bas van Fraassen, known for his anti-realism tied to the semantic conception of theories (Singh, 2012).

As it is surely no coincidence or miracle that scientific theories are so successful, Putnam (1975) argues that there must be plausible explanation for this, namely that the scientific theories are simply true. In virtue of IBE and some appeal to naturalism, one may therefore arguably discover just how satisfactory scientific realism is as an explanation of the success of scientific theories. They are just true, hence the success. The predictive success of science of course would be a miracle if predictively successful scientific theories were not (at least) approximately true. Yet this is not the case, and according to Putnam this is very good reason to endorse scientific realism. Consider Putnam’s (1975) slogan that realism “is the only philosophy that doesn’t make the success of science a miracle” (p. 73).


Scientific realism is concerned with (a) the epistemic achievements constituted by scientific theories and (b) the epistemic aims of scientific inquiry. On the former approach, scientific realism as discussed is the position concerning the actual epistemic status of theoriesi.e., the (approximate) truth of scientific theories or certain aspects of them. Semantically, this may be described in terms of the successful reference of theoretical terms to observable and unobservable things in the world. On the latter approach, scientific realism is then concerned with what science aims to do. According to the realist, this is to produce true descriptions of things in the world. What both approaches have in common is a commitment to the idea that the best scientific theories have a certain epistemic status: they yield knowledge of aspects of the world, including unobservable aspects (Chakravartty, 2017). This article, however, has explored the debate on scientific realism resulting from a tension between the empiricist methodology and claims to the effect that science can unveil the fundamental nature of reality (Ruyant, 2021). The realist position in this debate has been explored, in particular Putnam's intuition motivating realism known as the "no miracles" argument. Though this article has considered Putnam's (1975) argument as intuitively powerful, the no miracles argument is indeed contestable in a number of ways as antirealists will argue. Depending on how many scientific realist theses one denies, one has different "brands" of antirealism which object to Putnam’s argument and other realist variants alike. Scientific antirealism is discussed in the next article of this 101 series.

Bibliographical References

Chakravartty, A. (2017). Scientific Realism. In The {Stanford} Encyclopedia of Philosophy (Summer 2017). Metaphysics Research Lab, Stanford University.

Dawid, R., & Hartmann, S. (2018). The no miracles argument without the base rate fallacy. Synthese 195, 4063–4079.

Lipton, P. (2017). Inference to the best explanation. A Companion to the Philosophy of Science, 184–193.

Putnam, H. (1975). Mathematics, Matter and Method, Cambridge: Cambridge University Press.

Psillos, S. (1999). Scientific Realism: How Science Tracks Truth, London: Routledge.

Ruyant, Q. (2021). The Debates on Scientific Realism. In: Modal Empiricism. Synthese Library, vol 440. Springer, Cham.

Shand, J. & Bird, A. (2003). “Philosophy of Science,” in Fundamentals of Philosophy. 1st edn. London: Routledge.

Shapere, D. (1982). “The Concept of Observation in Science and Philosophy”, Philosophy of Science, 49(4): 485–525. doi:10.1086/289075

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Rebecca Ivory

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