Philosophy of science

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I believe that the philosophy of science is the metaphysics (comprising ontology, cosmology) and epistemology of science. Only by some such definition can the term 'philosophy of science' be given a meaning that will differentiate it from 'science' proper. From this point of view, moreover, the philosophy of science can enter into reciprocal relations -- amicable, I hope -- with science. It must absorb the results of science and it can offer methodological suggestions to science. But it does not need to be a postulate set for science from which specific matters of fact are to be derivable. Nor should one expect that philosophical issues are to be solved by going into the laboratory and setting up an experiment. The philosophical issues connected with science are about science, not in science. In the modern vernacular philosophical issues about science are meta-scientific and not scientific. Yet it remains true that the development of science is always the touchstone in terms of which to verify statements about science. In this sense the philosophy of science must be empirical and not merely tautological.
Louis Osgood Kattsoff[1] 

The philosophy of science is the study of the assumptions, foundations, and implications of science, including the formal sciences, natural sciences, and social sciences. It includes study of:

  • The nature of the terms, concepts, propositions, hypotheses, models and theories used by scientists.
  • How science explains natural phenomena and makes predictions.
  • The types of reasoning and arguments used to form scientific conclusions.
  • The formulation, scope, and limits of the scientific method.
  • The validity and objectivity of scientific statements, and.
  • The implications of scientific methods and models, along with the technology that arises from scientific knowledge, for society.

Issues of scientific ethics are not usually considered to be part of the philosophy of science; they are studied in such fields as bioethics and science studies.

History of philosophy of science

For more information, see: History of philosophy of science.

Philosophy of science has always been a part of philosophy and a part of the philosophy of several great philosophers during the ancient and middle ages. However in this time philosophy of science was quite premature. Modern science itself was highly induced by Roger Bacon's philosophy, which was in a large part philosophy of science. After this, a main debate of the still premature philosophy of science was the rationalism-empiricism debate, which lasted approximately until logical positivism synthesized both rationalism and empiricism in its logical-empiricist view. Logical positivism was the branch of philosophy, which developed philosophy of science to the level of a separate and mature branch of philosophy.

Nature of scientific concepts and statements

Science draws upon evidence from experimentation, logical deduction, and rational thought to examine the world. Science in general is the application of a logical frame of reference to a set of objects or situations. In other words, science is a method that is hard to define, but is not to be confused with the content or subject matter of any particular science.

Theory-dependence of observation

A scientific method depends on observation, in defining the subject under investigation and in performing experiments. Observation involves perception as well as a cognitive process: one does not make an observation passively, but is actively involved in distinguishing the thing being observed from surrounding sensory data. Therefore, observations depend on an understanding of how the world functions, and that understanding might influence what is perceived or deemed worthy of consideration. (See the Sapir-Whorf hypothesis for an early version of this understanding of the impact of cultural artifacts on our perceptions of the world.)

Empirical observation is used to test the truth of hypotheses within a theory. When someone claims to have made an observation, it is reasonable to ask them to justify that claim. Such a justification must make reference to the theory in which the observation is embedded; i.e., to some extent, the observation depends upon the theory that contains the hypothesis it either verifies or falsifies. However, this suggests that observation might not be a neutral arbiter between two theories; observation could only do this 'neutrally' if it were independent of the theories.

Thomas Kuhn denied that it is ever possible to isolate the theory being tested from the influence of the theory in which the observations are grounded. He argued that observations always rely on a specific paradigm, and that it is not possible to evaluate competing paradigms independently. By 'paradigm' he meant a logically consistent 'portrait' of the world, one that involves no logical contradictions. More than one such logically consistent construct can each paint a usable likeness of the world, but it is pointless to pit them against each other, theory against theory; neither is a standard by which the other can be judged. Instead, the question is which 'portrait' is judged by some set of people to promise most in terms of 'puzzle solving'.

For Kuhn, the choice of paradigm was sustained by, but not ultimately determined by, logical processes. The individual's choice between paradigms involves setting two or more 'portraits' against the world and deciding which likeness is most promising. In the case of a general acceptance of one paradigm or another, Kuhn believed that it represented the consensus of a community of scientists. Accepting or rejecting some paradigm is, he argued, more a social than a logical process.

That observation is embedded in theory does not mean that observations are irrelevant to science. Scientific understanding derives from observation, but the acceptance of scientific statements is dependent on the related theoretical background or paradigm as well as on observation. Coherentism and skepticism offer alternatives to foundationalism for dealing with the difficulty of grounding scientific theories in something more than observations.

Indeterminacy of theory under empirical testing

The Duhem–Quine thesis, after Pierre Duhem and W.V. Quine, points out that any theory can be made compatible with any empirical observation by the addition of suitable ad hoc hypotheses. This is analogous to the way in which an infinite number of curves can be drawn through any finite set of data points on a graph. This thesis was accepted by Karl Popper, leading him to reject naïve falsification in favour of 'survival of the fittest', or most falsifiable, of scientific theories. In Popper's view, any hypothesis that does not make testable predictions may be useful, but it cannot be said to be science. Confirmation holism, developed by W.V. Quine, states that empirical data are not sufficient to make a judgement between theories. A theory can always be made to fit with the available empirical data.

That empirical evidence does not serve to determine between alternate theories does not imply that all theories are of equal value. Rather than pretending to use a universally applicable methodological principle, the scientist makes a personal choice in choosing one particular theory over another (often using guiding principles such as Occam's razor). One result is that specialists in the philosophy of science stress that observations made for the purposes of science be restricted to intersubjective objects. That is, science is restricted to those areas where there is general agreement on the nature of the observations involved. It is comparatively easy to agree on observations of physical phenomena, harder to agree on observations of social or mental phenomena, and very difficult to reach agreement on matters of theology or ethics.


A central concept in the philosophy of science is empiricism, the view that knowledge is derived from our experiences. Scientific hypotheses are developed and tested through empirical methods consisting of observations and experiments. Once reproduced widely enough, information from these comprises the evidence from which scientists develop theories that explain facts about the world. Observations involve perception, and so are themselves cognitive acts. That is, observations are embedded in our understanding of the way in which the world works; as this understanding changes, the observations themselves might change. More accurately, our interpretation of observations may change. A well-designed experiment will produce similar results when carried out in a similar way. When the social context of the observer is a factor in an observation, objectivity is lost, and the observation is no longer scientifically useful.

Scientists attempt to use induction, deduction and quasi-empirical methods, and invoke key conceptual metaphors to work observations into a coherent, self-consistent structure.

Scientific realism and instrumentalism

Scientific realism is the view that the universe really is as explained by scientific statements. Realists hold that things like electrons and magnetic fields actually exist. By contrast, instrumentalism holds that our perceptions, scientific ideas and theories do not necessarily reflect the real world accurately, but are useful instruments to explain, predict and control our experiences. To an instrumentalist, electrons and magnetic fields are convenient ideas that might or might not actually exist. For instrumentalists, the empirical method is used to do no more than show that theories are consistent with observations. Instrumentalism is largely based on John Dewey's philosophy and, more generally, pragmatism, which was influenced by philosophers such as William James and Charles Sanders Peirce.

Social constructivism

One area of interest among historians, philosophers, and sociologists of science is the extent to which scientific theories are shaped by their social and political context. This approach is usually known as social constructivism. Social constructivism is in one sense an extension of instrumentalism that incorporates the social aspects of science. In its strongest form, it sees science as merely a discourse between scientists, with objective fact playing a small role if any. A weaker form of constructivism might hold that social factors play a large role in the acceptance of new scientific theories.

Analysis and reductionism

Analysis is the activity of breaking an observation or theory down into simpler concepts in order to understand it. Analysis is as essential to science as it is to all rational enterprises. It would be impossible, for instance, to describe mathematically the motion of a projectile without separating out the force of gravity, angle of projection and initial velocity. Only after this analysis is it possible to formulate a theory of motion.

Reductionism in science can have several different senses. One type of reductionism is the belief that all fields of study are ultimately amenable to scientific explanation. Perhaps a historical event might be explained in sociological and psychological terms, which in turn might be described in terms of human physiology, which in turn might be described in terms of chemistry and physics. The historical event will have been 'reduced' to a physical event. This might be seen as implying that the historical event was 'nothing but' the physical event, denying the existence of emergent phenomena.

Daniel Dennett invented the term greedy reductionism to describe the assumption that such reductionism was possible. He claims that it is just 'bad science' to seek explanations which are appealing or eloquent, rather than those that are of use in predicting natural phenomena. He also says that:

There is no such thing as philosophy-free science; there is only science whose philosophical baggage is taken on board without examination.Daniel Dennett, Darwin's Dangerous Idea, 1995.

Arguments against greedy reductionism through reference to emergent phenomena rely upon the fact that self-referential systems can be said to contain more information than can be described through individual analysis of their component parts. Examples include systems that contain strange loops, fractal organisation and strange attractors in phase space. Analysis of such systems is necessarily information-destructive because the observer must select a sample of the system that can be at best partially representative. Information theory can be used to calculate the magnitude of information loss and is one of the techniques applied by Chaos theory.

Grounds of validity of scientific reasoning

The most powerful statements in science are those with the widest applicability. Newton's Third Law — "for every action there is an opposite and equal reaction" — is a powerful statement because it applies to every action, anywhere, and at any time. But it is not possible for scientists to have tested every incidence of an action, and found a reaction. How is it, then, that they can assert that the Third Law is true? They may have tested many actions, but can we be sure that the next time we test the Third Law, it will hold true?

One solution is to rely on induction. Inductive reasoning maintains that if a situation holds in all observed cases, then it holds in all cases. So, after 'enough' experiments that support the Third Law, one is justified in maintaining that the Law holds in all cases. Justifying induction has been problematical however: no matter how often biologists observed white swans, and in how many different locations, there is no deductive path that can lead to the conclusion that all swans are white. Similarly, it is possible that an observation tomorrow will show an action that is not accompanied by a reaction. The problem of induction is very important in the philosophy of science: is induction indeed justified, and if so, how?

Critical rationalism

Sir Karl Raimund Popper, one of the most influential philosophers of science of the 20th century, is perhaps best known for repudiating the classical account of the scientific method by advancing empirical falsifiability as way to distinguish scientific theory from non-science, coining the term critical rationalism to describe his philosophy. Popper held that scientific theories are universal in nature, and can be tested only indirectly, by reference to their implications. He also held that scientific theory (and human knowledge generally) is irreducibly conjectural or hypothetical, and is generated by the creative imagination to solve problems that have arisen in specific historico-cultural settings. Logically, no number of positive outcomes at the level of experimental testing can confirm a scientific theory, but a single counterexample is decisive: it shows the theory to be false. Popper's account of the logical asymmetry between verification and falsification is at the heart of his philosophy, and it inspired him to take falsifiability as his criterion of demarcation between what is and is not scientific: a theory is scientific if and only if it is falsifiable. This led him to criticise both psychoanalysis and contemporary Marxism as pseudoscientific, on the basis that their theories are not falsifiable. Popper also wrote extensively against the Copenhagen interpretation of quantum mechanics. He strongly disagreed with Niels Bohr's instrumentalism, and supported Albert Einstein's realist approach to scientific theories of the universe.

The principle of falsifiability states that a scientific statement ('fact', theory, 'law', principle, etc) must be falsifiable, that is, able to be tested and disproved. Popper described falsifiability using the following observations, paraphrased from 'Conjectures and Refutations':

  1. It is easy to confirm or verify nearly every theory — if we look for confirmations.
  2. Confirmations are significant only if they are the result of risky predictions; that is, if, unenlightened by the theory, we should have expected an event which was incompatible with the theory — an event which would have refuted the theory.
  3. "Good" scientific theories include prohibitions which forbid certain things to happen. The more a theory forbids, the better it is.
  4. A theory which is not refutable by any conceivable event is non-scientific. Irrefutability is not a virtue of a theory.
  5. Every proper test of a theory is an attempt to falsify or refute it. Theories that take greater 'risks' are more testable, more exposed to refutation.
  6. Confirming or corroborating evidence is only significant when it is the result of a genuine test of the theory; 'genuine' in this case means that it comes out of a serious but unsuccessful attempt to falsify the theory.
  7. Some genuinely testable theories, when found to be false, are still upheld by their advocates — for example by introducing ad hoc some auxiliary assumption, or by reinterpreting the theory in such a way that it escapes refutation. Such a procedure is always possible, but it rescues the theory from refutation only at the cost of lowering its scientific status.

Despite criticisms of falsifiability by philosophers, it remains a cornerstone of the working philosophy of many scientists.


Induction and falsification both try to justify scientific statements by reference to other scientific statements. Both must avoid the problem of the criterion, in which any justification must in turn be justified, resulting in an infinite regress. The regress argument has been used to justify one way out of the infinite regress, foundationalism. Foundationalism claims that there are some basic statements that do not require justification. Both induction and falsification are forms of foundationalism in that they rely on basic statements that derive directly from observations.

The way in which basic statements are derived from observation complicates the problem. Observation is a cognitive act: it relies on our existing understanding, our set of beliefs. For example, an observation of a transit of Venus requires many auxiliary beliefs, such as those that describe the optics of telescopes, the mechanics of the telescope mount, and an understanding of celestial mechanics. At first sight, the observation does not appear to be 'basic'. Coherentism offers an alternative by claiming that statements can be justified by their being a part of a coherent system. In the case of science, the system is usually taken to be the set of beliefs of an individual or of the community of scientists. W. V. Quine argued for a Coherentist approach to science. An observation of a transit of Venus is justified by its being coherent with our beliefs about optics, telescope mounts and celestial mechanics. Where this observation is at odds with one of these auxiliary beliefs, an adjustment in the system will be required to remove the contradiction.

Ockham's razor

William Ockham (c. 1295–1349) … is remembered as an influential nominalist, but his popular fame as a great logician rests chiefly on the maxim known as Ockham's razor: Entia non sunt multiplicanda praeter necessitatem. No doubt this represents correctly the general tendency of his philosophy, but it has not so far been found in any of his writings. His nearest pronouncement seems to be Numquam ponenda est pluralitas sine necessitate, which occurs in his theological work on the Sentences of Peter Lombard (Super Quattuor Libros Sententiarum (ed. Lugd., 1495), i, dist. 27, qu. 2, K). In his Summa Totius Logicae, i. 12, Ockham cites the principle of economy, Frustra fit per plura quod potest fieri per pauciora. (Kneale and Kneale, 1962, p. 243).

Scientific inquiry typically involves a number of heuristic principles that guide the work. Prominent among these are the principles of conceptual economy or theoretical parsimony that are customarily placed under the rubric of Ockham's razor, named after the 14th century Franciscan friar William of Ockham. The motto is most commonly cited as "entities should not be multiplied beyond necessity", generally taken to suggest that the simplest explanation tends to be the correct one. As interpreted in contemporary scientific practice, it advises choosing the simplest theory among a set of competing theories that have a comparable explanatory power, discarding assumptions that do not improve the explanation. The "other things being equal" clause is a critical qualification, which limits the utility of Ockham's razor in real practice, as theorists rarely find themselves presented with competent theories of exactly equal explanatory adequacy.

Among the difficulties of trying to apply Ockham's razor is the problem of formalizing the measure of simplicity. Although various measures have been proposed, it is generally recognized that there is no such thing as a theory-independent measure of simplicity: there appear to be as many different measures as there are theories. Moreover, it is difficult to identify the hypotheses or theories that have comparable explanatory power, although it may be possible to rule out some extremes. Ockham's razor also does not say that the simplest account is to be preferred regardless of its capacity to explain exceptions, or other phenomena. The principle of falsifiability requires that any exception that can be reliably reproduced should invalidate the simplest theory, and that the next-simplest account which can actually incorporate the exception as part of the theory should then be preferred. As Albert Einstein puts it, "The supreme goal of all theory is to make the irreducible basic elements as simple and as few as possible without having to surrender the adequate representation of a single datum of experience".

Social accountability

As the areas for science to investigate are potentially infinite, the issue arises as to what should science attempt to question or find out. Philip Kitcher in his Science, Truth, and Democracy[2] makes an important point about openness in science suggesting that scientific studies that attempt to show one segment of the population as being less intelligent, successful or emotionally backward compared to others, has a political feedback effect which further excludes such groups from access to science. Thus such studies undermine the broad consensus required for good science by excluding certain people, and so proving itself in the end to be unscientific.

A critical question is, to what degree the current body of scientific knowledge can be taken as an indicator of what is 'true' about the physical world in which we live? The acceptance of such knowledge as if it were absolutely true and unquestionable (in the sense of theology or ideology) has been called scientism.

However, it is common for members of the public to have the opposite view of science — many lay people believe that scientists are making claims of infallibility. Science serves in the process of consensus decision making by which people of varying moral and ethical views come to agree on 'what is real'. In secular and technological societies, without any stronger conception of reality based on other shared ethical or moral or religious grounds, science has come to serve as the primary arbiter in disputes. This leads to the abuse of scientific dialogue for political or commercial ends. Concern about the wide disparity between how scientists work and how their work is perceived has led to public campaigns to educate lay people about scientific skepticism and the scientific method.

Critiques of science

Paul Feyerabend argued that no description of scientific method could be broad enough to encompass all the approaches and methods used by scientists. Feyerabend objected to prescriptive scientific method on the grounds that any such method would stifle and cramp scientific progress. Feyerabend claimed, "the only principle that does not inhibit progress is: anything goes."

Sociology and anthropology of science

In his book The Structure of Scientific Revolutions[3] Kuhn argues that observation and evaluation always take place within a paradigm. "A paradigm is what the members of a community of scientists share, and, conversely, a scientific community consists of men who share a paradigm". For Kuhn the fundamental difference between science and other disciplines is in the way in which the communities function. Others, especially Feyerabend and some post-modernist thinkers, have argued that there is insufficient difference between social practices in science and other disciplines to maintain this distinction. It is apparent that social factors play an important and direct role in scientific method, but that they do not serve to differentiate science from other disciplines.

A major development in recent decades has been the study of the formation, structure, and evolution of scientific communities by sociologists and anthropologists including Michel Callon, Elihu Gerson, Bruno Latour, John Law, Susan Leigh Star, Anselm Strauss, Lucy Suchman, and others. Some of their work has been previously loosely gathered in actor network theory. Here the approach to the philosophy of science is to study how scientific communities actually operate. More recently Gibbons and colleagues (1994) have introduced the notion of mode 2 knowledge production. Researchers in Information science have also made contributions, e.g., the Scientific Community Metaphor.

Continental philosophy of science

In the Continental philosophical tradition, science is viewed from a world-historical perspective. One of the first philosophers who supported this view was Georg Wilhelm Friedrich Hegel, and Ernst Mach, Pierre Duhem and Gaston Bachelard also adopted this approach to science. Nietzsche advanced the thesis in his "The Genealogy of Morals" that science was a new form of religion. All of these approaches involve a historical and sociological turn to science, with emphasis on lived experience (a kind of Husserlian "life-world"), rather than a progress-based or anti-historical approach as done in the analytic tradition. Two other approaches to science include Edmund Husserl's phenomenology and Martin Heidegger's hermeneutics.

The largest effect on the continental tradition with respect to science was Martin Heidegger's assault on the theoretical attitude in general which of course includes the scientific attitude. For this reason one could suggest that the philosophy of science, in the Continental tradition, has not developed much further due to its inability to overcome Heidegger's criticism.

Notwithstanding, there have been a number of important works: especially a Kuhnian precursor, Alexandre Koyré. Another important development was that of Foucault's analysis of the historical and scientific thought in The Order of Things and his study of power and corruption within the "science" of madness.

Philosophy of science by scientists

Many scientists who were not trained as philosophers have commented extensively on the philosophy of science as it relates to their particular discipline. Albert Einstein, for example, wrote a number of popular works that included speculations on the nature of science and its relationship to theology, and Stephen Jay Gould commented on similar issues regarding biology. For many scientists, the philosophical musings of well-known and eloquent scientists are more accessible and more relevant to their work than those of philosophers, who generally write for an audience of fellow philosophers.

More recently, the battles over teaching evolution and intelligent design in the public schools have brought some philosophical issues to the fore (most notably, "What makes an area of study scientific?"), and practicing biological and geological scientists have found themselves being asked, along with philosophers, to comment on matters that are at least as much philosophy as biology.

References and notes

  1. Kattsoff LO. (1957) Physical Science and Physical Reality. The Hague: Nijhoff.
  2. Kitcher P (2001) Science, Truth, and Democracy. Oxford: Oxford University Press. | Google Books preview.
    • From "Introduction": From time to time, when I explain to a new acquaintance that I'm a philosopher of science, my interlocutor will nod agreeably and remark that surely means I'm interested in the ethical status of various kinds of scientific research, the impact that science has had on our values, or the role that the sciences play in contemporary democracies. Although this common response hardly corresponds to what professional philosophers of science have done for the past decades, or even centuries, it is perfectly comprehensible. For there are large questions of the kinds just indicated, questions that deserve to be posed and answered, and an intelligent person might well think that philosophers of science are the people who do the posing and the answering. The chapters that follow are a first attempt to do just that.
  3. Thomas S Kuhn (2008). Francis Wilson Smith, Thomas Bender (eds.): American higher education transformed, 1940-2005: documenting the national discourse, Reprint of The structure of scientific revolutions (1966). John Hopkins University Press, p. 241 ff. ISBN 0226458083.