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The neutrality of this article is disputed.
The scientific method is a sequence or collection of procedures that are considered characteristic of
scientific investigation and the acquisition of new scientific knowledge based upon physical evidence. This method is believed to distinguish science
from other intellectual traditions, such as painting, philosophy or theology.
History
In his enunciation of a 'scientific method' in the thirteenth
century, Roger Bacon was inspired by the writings of Arab alchemists, who had preserved and built upon Aristotle's portrait of induction. Bacon
described a repeating cycle of observation, hypothesis, experimentation, and the need for independent
verification. In the 17th century Francis Bacon described a
rational procedure for establishing causation between phenomena. Argument by analogy, which was popular in the ecclesiastical
scholarly tradition, became much less acceptable in science (or "natural philosophy," as it was still called).
It is common to speak as though a single approach such as Roger Bacon's is how scientists operate all the time. Many
scientists, historians, philosophers and sociologists regard this perspective as naïve, and see the actual operation of science as more
complicated and haphazard. A common element of scientific research involves the vetting of theories in a way that seems more
formal and rigorous than the practices of other disciplines and traditions.
In the twentieth century Karl Popper introduced the idea that a hypothesis
must be falsifiable; that is, it must be capable of being demonstrated
wrong. This was similar to C S Peirce's position, falibilism, which Popper credited after he
became aware of Peirce's work. Today falsifiability is often cited as a main distinction between science and pseudoscience.
The question of how science operates has importance well beyond scientific circles
or the academic community. In the judicial system and in public policy controversies, for example, a study's deviation from
accepted scientific practice is grounds for rejecting it as "junk
science" or pseudoscience. Whether formularizable or not, scientific
method is presented as a standard of proficiency and reliability.
The idealized scientific method
The essential elements of the scientific method are conventionally described as follows:
- Observation
- Hypothesis/Prediction
- Experimentation
- Conclusion and evaluation
- Repetition
This can be called the hypothetico-deductive
method. These activities do not describe all that scientists do. The simplified method described above is often used in
education. Teachers using inquiry as a teaching method sometimes teach a
slightly modified version of the scientific method in which "Question" is substituted for Observation. Many schools unfortunately
gloss over the step of "Repeat" due to time constraints.
Science is a social activity. A scientist's theory or proposal is accepted only after it has become known to others (usually
via publication, ideally peer reviewed publication) and criticised.
Some, who call themselves scientists but do not observe the above methodology (such as astronomers and social scientists), criticise this as
being an overly prescriptive and narrow interpretation of science.
The scientific method begins with an observation of some phenomenon. Observation often demands careful measurement. This guides the researcher to begin a further investigation.
Without the initial observation, there is no reason to begin the process. This stage may instead be called "Questioning," in
which the scientist or student realizes they have a question about a topic that can only be answered by doing an experiment of
some type.
Operational definitions of measurements and
other relevant concepts are not scientific hypotheses; they are not "falsifiable"; they are simply a way to ensure that everyone
is talking about, experimentally testing, etc the same thing. By definition, words acquire exact meanings which do not
necessarily correspond with their use in natural language: for
example, mass and weight are
quite distinct concepts, but the distinction is often ignored in everyday life.
New theories may arise when it is realised that words used have not previously been clearly defined. For example, Albert Einstein's first paper on relativity begins by defining simultaneity and the means
for determining length (which were skipped over by Isaac Newton with I do not define time, space, place and motion, as being well known to all) and proceeds to demonstrate that, given these
definitions, certain widely accepted ideas (absolute time; length independent of motion) were invalid.
A hypothesis is a suggested explanation of the observations. It needs to be consistent with the phenomenon or set of facts
observed. Sometimes this is nothing more than a "guess," especially in the case of students. Scientists use whatever they
can—their own creativity (currently not well understood), ideas from other fields, induction, or even systematic guessing, or any other methods available—to come up with possible
explanations for the phenomenon under study. There are no definitive guidelines for the production of new hypotheses. The history
of science is filled with stories of scientists claiming a "flash of inspiration", or a hunch, which then motivated them to look
for evidence to support or refute their idea. Michael Polanyi made
such creativity the centrepiece of his discussion of methodology.
A specific prediction should arise (as a logical consequence of the hypothesis), that can be put to the test of an experiment,
which should allow concrete measurements. If results contradictory to the predictions are found, the hypothesis under test is
incorrect or incomplete, requiring either revision or abandonment. If results consistent with the hypothesis are found, the
hypothesis might be correct, but is always subject to further tests. Deductive reasoning is the way in which predictions are developed with which to test a hypothesis.
In our example of Einstein's General Relativity, his theory makes several specific predictions about the observable structure
of space-time, such as a prediction that light bends in a gravitational field, and that the amount of bending depends in a precise way on the strength of the
gravitational field. Observations made during a 1919 solar eclipse supported the hypothesis (i.e., General Relativity) as against those of other hypotheses which
predicted different results, and falsified any theory which predicted something else, e.g., Newtonian gravitation.
Once a prediction or set of predictions are made, an experiment must be
designed to test those predictions. It is often easier to disprove a hypothesis than to support it, as less precision in
measurements may be needed. Ideally, the experiments performed should be fully described so that anyone can reproduce them, and
many scientists should independently verify every hypothesis. Results that can be obtained from experiments performed by many are
termed reproducible and are given much greater weight in evaluating hypotheses than non-reproducible results.
Scientists must design their experiments carefully. For example, if the measurements are difficult to make, or subject to
observer bias, one must be careful to avoid distorting the results because of influences that arise from the experimenter's
wishes. When experimenting on complex systems, one must be careful to isolate the effect being tested from other possible causes
of the intended effect (this results in a controlled experiment).
In testing a drug, for example, it is important to carefully test that the supposed effect of the drug is produced only by the
drug itself, and not by the placebo effect or by random chance. Doctors
do this with what is called a double-blind study: two groups of patients are compared, one of which receives the drug and one of
which receives a placebo. No patient in either group knows whether or not they are getting the real drug. Even the doctors or
other personnel who interact with the patients do not know which patients are getting the drug under test and which are getting a
fake drug (often sugar pills), so their knowledge cannot influence the patients.
Conclusion and evaluation
Once the experiment is complete, the researcher determines whether the results (or data) gathered are what was predicted.
Failure to see the predicted results from a well designed and implemented experiment is clear indication that the hypothesis is
defective. If instead one sees the predicted results, this is an indication that the hypothesis is acceptable though not
'confirmation' or 'proof' of its correctness. Other possible explanations of the result must also be examined. Only when no
better theory presents itself can you be reasonably sure your hypothesis is correct.
Repetition / reproduction
Repetition implies one of two possible actions:
- If the experimental conclusions fail to match the predictions/hypothesis, then in the idealised model one returns to the
start to repeat the entire process.
- If the experiment(s) appears "successful" - i.e. fits the hypothesis - then the results are to be published in a way which
allows others (in theory) to reproduce the same experiments and results.
The second sense implies that the theory and experimental methods should be described in sufficient detail, and widely
disseminated, to allow a competent and sufficiently equipped scientist or team to repeat/verify the results. Reproducibility is
easy in simple cases - the chemical analysis of a salt, for example, where materials and techniques are readily accessible. In
more complex cases it becomes blurred: there may be only one particle accelerator in the world capable of doing certain
experiments. In either case, it is important that the experiments be sufficiently well described to be reproducible in principle even if they cannot be repeated in
practice.
Probably the most important aspect of scientific reasoning is the demand for empirical outside verification: the experiment
must be repeatable by other researchers, and their results must be the same for your conclusions to be valid. Verification is the
process of determining whether the hypothesis is in accord with empirical evidence, both newly acquired and already existing. It
is the necessary complement to predictions.
Falsificationism requires that any hypothesis, no matter how respected or time-honoured, be discarded once it is contradicted
by reliable evidence, evidence that usually would come from new experiments. This is something of an oversimplification, since
individual scientists will often hold on to their pet theory long after contrary evidence has been found. Max Planck is said to have suggested that new scientific theories are adopted when
today's scientists finally die. This is not always a bad thing -- delayed adoption, not scientist mortality. Any theory can be
made to correspond to the facts, simply by making a few adjustments—called "auxiliary hypotheses"—so as to bring it
into correspondence with the accepted observations. When to reject one theory and accept another ('better' one) is dependent on
the judgement of individual scientists, rather than on some law or authority.
A popular example of this is the so-called "turtle theory" that the
Earth is flat and suspended on the backs of turtles. When asked why we can't see or feel these turtles, believers of turtle
theory will modify their statement to say that the turtles are invisible, or intangible. As for the turtles, the members of the
Flat Earth Society apparently still regard it as a tenable
hypothesis, despite any observations made in the last few thousand years that might contradict it.
All scientific knowledge is thus always in a state of flux, for at any time new evidence could be
presented/discovered/developed that contradicts a long-held hypothesis. A particularly luminous example is the theory of light. Light had long been supposed to be made of particles. Isaac Newton, and before him many of the Classical Greeks, was convinced it was so, but his light-is-particles
account was overturned by evidence in favor of a wave theory of
light suggested most notably in the early 1800s by Thomas Young an
English physician. Light as waves neatly explained the observed diffraction and interference of light when, to the contrary, the
light-as-a-particle theory did not. The wave interpretation of light was widely held to be unassailably correct for most of the
19th century. Around the turn of the century, however, observations were made that a wave theory of light could not explain. This
new set of observations could be accounted for by Max Planck's quantum theory
(including the photoelectric effect and Brownian motion—both from Albert Einstein), but not by a wave theory of light. Nor, for that matter, by the particle theory.
The failure of one hypothesis often does not lead smoothly to a new and successful hypothesis. In the case of light, the
result of the ferment created by the two contrary sets of very well verified observations was the slow birth of quantum mechanics.
Experiments, whether widely accepted or not, should be performed by many different scientists so as to guard against bias,
error, misunderstanding, fraud, etc. Those that seem to call into question, or even force rejection of, an existing previously
satisfactory theory should be especially carefully checked. Scientific journals use a process of peer review, in which scientists' papers describing experimental results and their conclusions are
submitted to a panel of fellow scientists for evaluation.
Scientists are rightly suspicious of results that do not go through this process. For example, the cold fusion experiments of Fleischmann and Pons were never peer reviewed—they were announced
directly to the press before any other scientists were able to evaluate their efforts or reproduce their results. Their results
have not been reproduced elsewhere else in the decades since; the press announcement was regarded at the time, by most nuclear physicists, as very likely wrong. Peer review may well have turned up
problems and led to a closer examination of the experimental evidence Fleischmann, Pons, et al. believed they had found. Paul Kammerer's experiments on acquired physical
traits in amphibians (described in Arthur Koestler's The Midwife
Toad) seem to have been deliberately faked, while the confusion in the 60s and 70s about 'polywater' seems to have been the result of micro contamination. Much embarrassment and wasted effort might have
been avoided by proper peer review in many such cases.
On the other hand, peer review of new discoveries is sometimes not very open-minded. The proposed existence of infectious protein particles by Stanley Prusiner in 1982 caused much scoffing and even hostility
since it seemingly contradicted the central dogma of molecular biology, yet he won the 1997 Nobel Prize
in physiology or medicine for the discovery of prions. Similarly, dark matter wasn't believed when first theorized in 1933 by Fritz Zwicky, nor when observationally confirmed by
Vera Rubin in 1978, but after multiple
independent confirmations, dark matter is now accepted in astrophysics.
Scientific method and the practice of science
The primary constraints on science are:
- Publication, i.e. Peer review
- Resources (mostly, funding)
It has not always been like this: in the old days of the "gentleman scientist" funding (and to a lesser extent publication)
were far weaker constraints.
Both of these constraints indirectly bring in the idealised method - work that too obviously violates the constraints will be
difficult to publish and difficult to get funded. Journals do not require submitted papers to conform to anything more specific
that "good scientific practice" and this is mostly enforced by peer review. Originality, importance and interest are more
important - see for example the author guidelines for Nature.
Scientists tend to look for theories that are "elegant" or "beautiful". In contrast to the usual English use of these terms, scientists have more
specific meanings in mind. "Elegance" (or "beauty") refers to the ability of a theory to neatly explain all known facts as simply
as possible, or at least in a manner consistent with Occam's Razor
while at the same time being aesthetically pleasing. This seems to be primarily a psychological bias, however often it has been
useful in predicting correctly among competing theories. After all, 'more complex' (and so less psychologically satisfying)
theories have often been required 'to account for the phenomena'. Superstring theory (even with all those dimensions) may turn
out to be a theory which is both beautiful and yet as lean as it possibly could be. Turtlian world support theory has not been
widely praised for either its predictive successes or its aesthetic qualities.
Bayesian methodology
Bayesian inference has been claimed as a suitable logical
basis for discriminating between conflicting hypotheses. This method uses an estimate of the degree of belief in a hypothesis
before the advent of some evidence to give a numerical value to the degree of belief in the hypothesis after the advent of the
evidence. Bayesians claim to have provided a general solution to the Quine-Duhem thesis.
Philosophical issues
The study of the scientific method is distinct from the practice of science and is more a part of the philosophy, history and
sociology of science than of science itself. Such studies have limited direct impact on day-to-day scientific practice.
What has been called idealised scientific method in this article is one of many theories describing the way in which
science works or should be conducted. These include hypothetico-deductive method, falsifiability, the research programs of Imre Lakatos,
and the scientific revolutions of Thomas Samuel Kuhn. It seems
reasonable to ask how accurate it is in portraying the actual procedures followed by working scientists.
The material presented below is intended to show that, as with all philosophical topics, some of the issues surrounding the scientific method are neither
straightforward nor simple.
Verification
The idealised scientific method claims to rely on observation as a main component of the process of verification.
Observation involves perception, and so is a
cognitive process. That is, one does not make an observation
passively, but is actively involved in distinguishing the thing being observed from surrounding sensory data. Observations,
therefore, depend on some underlying understanding of the way in which the world functions, and that understanding may influence
what is perceived, noticed, 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.)
So observations are embedded in theory. The idealised scientific method uses empirical observation to determine the
acceptability of hypotheses during the verification phase. Observation could only do this neutrally if the theory on which the
observation depends and the theory being verified were independent of each other.
Kuhn denied that it is ever possible to isolate the theory being tested
from influence by the theory in which the making of observations is grounded, arguing that observations always rely on a specific
paradigm, and that it is not possible to evaluate competing paradigms independently. By "paradigm" he meant, essentially, a
logically consistent "portrait" of the world, one that involves no logical contradictions. More than one such logically
consistent construct can 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 the 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 the
community of scientists. Acceptance or rejection of some paradigm is, he argued, more a social than a logical process.
The Quine-Duhem
thesis claims that any theory can be made compatible with any empirical observation by the addition of suitable ad hoc
hypotheses. 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
is simply not science. Something else useful and valuable perhaps (or perhaps not), but not science.
Confirmation holism, a theory developed by W. V. Quine and well accepted among professional philosophers of science, states that
empirical data is not sufficient to make a judgment between theories. A theory can always be made to fit with the empirical data
available. Thus, shaping
principles play a predominate role in what theories are accepted into the scientific community.
Foundationalism
The idealised method adopts a foundationalist epistemology, explicitly claiming that observation is needed to get the scientific
process underway, and implicitly claiming that observations do not require justification.
It was noted above that observation is embedded in theory. It is reasonable, when someone claims to have made an observation,
to ask them to justify their claim. Such a justification must itself make reference to the theory - the operational definitions
and deductions from hypotheses - in which the observation is embedded. But this means, again, that observation by itself cannot
be used to decide between competing theories.
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 a well as on observation. Coherentism and scepticism offer alternative ways of dealing with the difficulty of grounding scientific theories in
something more than observations.
One result of this dilemma is that most specialists in the philosophy of science stress the requirement that observations made
for the purposes of science be restricted to intersubjective objects
Demarcation
Scientific Method is often touted as determining which disciplines are scientific and which are not. Those which follow the
scientific method might be considered sciences; those that do not are not. That is, method might be used as the criterion for
demarcation between science and non-science.
If observation cannot act as a theory-independent foundation for the scientific enterprise,
science becomes a cycle of hypothesising and verification embedded in a theoretical framework and tied to the 'real world' by the
agreement of the scientific community. Popper's claim that only falsifiable statements are scientific does not help here (see
The Criterion of Demarcation). The
Quine-Duhem thesis argues that it is not possible to prove that a statement is falsified; rather, falsification occurs
when the scientific community agrees that a statement is falsified.
Assuming this to be true, it is not obvious how scientific debate differs in any logical way from the debates of, for example,
historians. Both work within a cycle of hypothesising and verification, historians by reference to historical documents,
scientists by reference to the experiments they construct. It is not possible to conduct experiments to test historical
hypotheses, and that is not what this argument claims. History has already happened and cannot be rerun. Historians test their
hypotheses by comparing them to historical sources and to other theories, whilst scientific theories are tested by comparing them
to experimental results. What appears to differ is not the method, but the content, with historians taking historical documents
as their verification criterion, while scientists use documentation from experiments.
One might argue that science occupies a special place because its experiments can be repeated, but using repetition as a
demarcation criterion would disenfranchise areas that are at present considered to be science, such as palaeontology and
cosmology.
Alternately, Kuhn claims that the explanatory success of science is explained by the way in which scientists are restricted to
working within a particular paradigm.
Paul Feyerabend takes these arguments to their limit, arguing that
science does not occupy a special place in terms of either its logic or method, and so that any claim to special authority made
by scientists cannot be upheld. This leads to a particularly democratic and anarchist approach to knowledge formation.
Quality of evidence
Evidence comes in different forms and quality, mostly due to underlying assumptions. If a theory uses as underlying assumption
that 'objects heavier than air fall to the ground when dropped', this requires no further proof. An underlying assumption like
'aliens abduct humans' however is an extraordinary claim which requires extraordinary proof. Example: if the news reports that a
known consertive politician has voted against legislation that would legalize marijuana in the USA, the basic underlying
assumption (the voting behaviour of the conservative) complies with what we know about politics and can therefor be given a high
probability of being true. The news is a fairly reliable source, the statement can therefor be taken as true without further
evidence. If however this same newsprogram then reports that 94 year old man has run the marathon in under 1 hour (while the
world record is around 2 hours), this can not be taken as true, although the source is the same. This is an extraordinary claim
and therefor requires extraordinary proof. Most extraordinary claims also do not survive Occam's razor.
Science as a communal activity
The idealised scientific method makes reference to the scientific community in the verification and evaluation of a
scientific theory. Some consideration will lead to the conclusion that the role of the scientific community extends further than
this.
In his book The
Structure of Scientific Revolutions Kuhn argues that the process of observation and evaluation 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' (postscript, part 1). On this account, science can be done only as a part of a community, and is
inherently a communal activity.
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.
This is not an area of study in which it is possible to give a definitive account, because it is undergoing considerable
change. It appears that positivist, empiricists and falsificationist theories are unable to satisfy their aim of giving as
definitive account of the logic of science; it may also be that the sociology of science is incapable of accounting for the
success of the scientific enterprise. In any case, it should be clear that the idealised scientific method is a source of ongoing
debate and contention.
Annotated list of related issues
Empirical methods
Paradigm change
- Paradigm, perhaps the most abused word in English.
- Thomas Kuhn wrote influentially on the sociology of scientific
revolutions in The
Structure of Scientific Revolutions.
- Paradigm shift is a Kuhnian term referring to the change between
one pervasively accepted theory (eg, Aristotian motion) and another (eg, Newtonian gravitation). Kuhn himself came to prefer
other terminology.
The problem of induction questions the logical ground
for induction as a basis for science.
- Inductive reasoning has appeared to some (most famously,
to Sir Francis Bacon) to be at the core of scientific method; it also appears to be logically invalid.
- David Hume was the person who most famously and influentially pointed out
the inadequacy of induction in generating true statements, scientific or not.
- Karl Popper offered one resolution, Falsifiability
- In his book Consilience:
The Unity of Knowledge biologist E. O. Wilson suggests that we can
validate the pragmatic value of induction by exploring the consilience of inductions obtained from different fields of
science.
Scientific creativity
When Method goes wrong
Other stuff
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