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Scientific Method

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Scientific method

The scientific method usually refers to either a series or a collection of processes that are considered characteristic of scientific investigation and of the acquisition of new scientific knowledge.

Philosophers, historians and sociologists have found many ways to describe the scientific process. Often when someone describes how they think science is done, they are describing how they think science may be best or most reliably done. As a result, discussions of scientific method are frequently partisan. Indeed, there are perhaps as many methods of doing science as there are methodologists.

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The enunciation of a scientific method by Roger Bacon in the thirteenth century described a repeating cycle of observation, hypothesis, experimentation and the need for independent verification. This view, itself inspired by an arab alchemical tradition not endorsed by christian ecclesiastical authority, led to Francis Bacon (in 1620 with the New Organon) laying down some methods for identifying causation between phenomena. With these articulations, unfounded speculation and analogical arguments began to be replaced by consistent and logical methods of investigation.

It is common to speak as if a single approach of this type were how scientists operate literally and all the time. Most historians, philosophers and sociologists regard this perspective as naïve, and view the actual progress of science as more complicated and haphazard. The actual course of scientific progress is inseparable from the politics and culture of science; a single, formal process cannot suffice either to explain or prescribe scientific progress.

The question of how science operates is important well beyond the academic community. In the judicial system and in policy debates, for example, a study's deviation from accepted scientific practice is grounds to reject it as "junk science." Whether strictly formularizable or not, science represents a standard of proficiency and reliability, and this is due at least in part to the way scientists work.

The idealized scientific method

The essential elements of the scientific method are traditionally described as follows:

  • Observe: Observe or read about a phenomenon.

  • Hypothesize: Wonder about your observations, and invent a hypothesis, a 'guess', which could explain the phenomenon or set of facts that you have observed.

  • Test

    • Predict: Use the logical consequences of your hypothesis to predict observations of new phenomena or results of new measurements.

    • Experiment: Perform experiments to test the accuracy of these predictions.

  • Conclude: Accept or refute hypothesis

    • Evaluate: Search for other possible explanations of the result until you can show that your guess was indeed the explanation, with confidence.

    • Formulate new hypothesis

These activities do not describe all that scientists do. This simplified method is useful for teaching, since it describes the way in which scientists often think of themselves as acting.

This idealised process is often misinterpreted as applying to scientists individually rather than to the scientific enterprise as a whole. Science is a social activity, and one scientist's theory or proposal cannot become accepted unless it has been published, peer reviewed, criticised, and finally accepted by the scientific community.


The scientific method begins with observation. Observation often demands careful measurement. It also requires the establishment of operational definitions of measurements and other relevant concepts. Definitions are not scientific hypotheses; they are not "falsifiable"; they are always true or tautological. Definitions condense a number of ideas into a single word or phrase. That being said, an observer's definition could differ significantly from commonly understood concepts of a term, and still be correct. Such a definition, however, would carry greater risk of being misunderstood. These definitions are operational in that they may differ with the context of a hypothesis, and they may be refined when the hypothesis is refined.

For example, the term "day" is useful in ordinary life and its meaning may vary with the context. (Do we mean a 24 hour period or do we mean the time between sunrise and sunset?) We don't have to define it precisely to make use of it. In many sciences it is precisely 86,400 atomic seconds. In studying the motion of the Earth, we may use two distinct operational definitions: a solar day is the time between two successive observations of the sun at the same position in the sky; a sidereal day is the time between two successive observations a specific star sky at the same position. The length of these two kinds of day differs by about four minutes.

Slight differences between operational definitions are often important, as they are needed to make experiments precise enough to distinguish subtle underlying phenomena. An example of this lies in choosing the appropriate segmentation in the statistical analysis of data. Distinctions in operational definitions can also reflect important conceptual differences: for example, mass and weight are regarded as quite different concepts in science, but the distinction is often ignored in everyday life.


To explain the observation, scientists use whatever they can (their own creativity (currently not well understood), ideas from other fields, or even systematic guessing, or any other methods available) to come up with possible explanations for the phenomenon under study.

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. Paul Feyerabend argued against this position, providing examples of falsified scientific theories that nevertheless had a vital role in the progress of scientific understanding.

Of course, it is impossible for the scientist to be impartial, considering all known evidence, and not merely evidence which supports the hypothesis under development. But by submitting their theories for peer review, scientists can at least make it more likely that the hypotheses formed will be relevant and useful, or at least get others to agree with it.

In the extremely rare cases where no better grounds for discriminating between rival hypotheses can be found, the bias scientists almost always follow is the principle of Occam's Razor; one chooses the simplest explanation for all the available evidence, in whatever sense "simple" is chosen to be defined (is it that which takes the fewest steps, or combines the smallest number of scientific facts, or takes the fewest words to express, or is the easiest to understand, or is the most predictable, or simply seems the most like common sense, or the average person's idea of common sense, to the scientist(s) judging the model?)


A hypothesis must make specific predictions; these predictions can be tested with concrete measurements to support or refute the hypothesis. For instance, Albert Einstein's General Relativity makes a few specific predictions about the structure of space-time, such as the prediction that light bends in a strong gravitational field, and 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 the other possible hypotheses which predicted different results. (Later experiments confirmed this even further.)

Deductive reasoning is the way in which predictions are used to test a hypothesis.


Probably the most important aspect of scientific reasoning is verification: The results of one's experiments must be verified. Verification is the process of determining whether the hypothesis is in accord with empirical evidence, and whether it will continue to be in accord with a more generally expanded body of evidence.

Ideally, the experiments performed should be fully described so that anyone can reproduce them, and many scientists should independently verify every hypothesis. Results which 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 by 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 don't know which patient is getting the drug under test and which is getting a fake drug (often sugar pills), so their knowledge can't influence the patients either.


Falsificationism argues that any hypothesis, no matter how respected or time-honoured, must be discarded once it is contradicted by new reliable evidence. This is of course an oversimplification, since individual scientists inevitably hold on to their pet theory long after contrary evidence has been found. This is not always a bad thing. Any theory can be made to correspond to the facts, simply by making a few adjustments—called "auxiliary hypothesis"—so as to bring it into correspondence with the accepted observations. The choice of when to reject one theory and accept another is inevitably up to the individual scientist, rather than some methodical law.

Hence all scientific knowledge is always in a state of flux, for at any time new evidence could be present that contradicts long-held hypotheses. A classic example is the explanation of light. Isaac Newton's particle paradigm was overturned by the wave theory of light, which explained diffraction, and which was held to be incontrovertible for many decades.The wave paradigm, in turn was refuted by the discovery of the photoelectric effect. The currently held theory of light holds that photons (the 'particles' of light) are both waves and particles; experiments have been performed which demonstrate that light has both particle and wave properties.

The experiments that reject a hypothesis should be performed by many different scientists to guard against bias, mistake, misunderstanding, and fraud. Scientific journals use a process of peer review, in which scientists submit their results to a panel of fellow scientists (who may or may not know the identity of the writer) 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 had tried to reproduce the results or evaluate their efforts. They have not been reproduced elsewhere as yet; and the press announcement was regarded, 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. Much embarrassment, and wasted effort worldwide, would have been avoided.

Other aspects of method

There are no definitive guidelines for the production of new hypotheses. The history of science is filled with stories of scientists describing 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 methodology.

The anecdote that an apple falling on Isaac Newton's head inspired his theory of gravity is a popular example of this (there is no evidence that the apple fell on his head; all Newton said was that his ideas were inspired "by the fall of an apple.") Kekule's account of the inspiration for his hypothesis of the structure of the benzene-ring (dreaming of snakes biting their own tails) is better attested.

Scientists tend to look for theories that are "elegant" or "beautiful"; in contrast to the usual English use of these terms, scientists have a more specific meaning in mind. "Elegance" (or "beauty") refers to the ability of a theory to neatly explain all known facts as simply as possible, or in a manner consistent with Occam's Razor.

The Ptolemaic model of the universe suggested that the earth is the centre of a pristine, perfect universe, and all motions in such a universe must be circular. The model explained the apparent retrograde motion of the planets, by introducing epicycles. Nicolaus Copernicus' model placed the sun at the centre of planetary motion, but also assumed that the planets moved in perfect circles. It also found it necessary to make use of epicycles, and was as complex as, yet less accurate than the heliocentric model. Improvement in the accuracy of the model depended not only on developing the mathematics of elliptical orbits, but a conceptual change in the way in which motion was understood. Tycho Brahe made unprecedentedly accurate observations, but did not reject the geocentric model. It took Kepler 20 years to formulate equations which explained Tycho Brahe's observations in heliocentric terms.

Isaac Newton's System of the World unified Kepler's laws and Galileo's mechanical studies of acceleration, which re-integrated modern science into a comprehensible world model.

Dogged adherence to method can be counterproductive.

History is replete with examples of accurate theories ignored by peers, and inaccurate ones propagated unduly.

Often it is the less accurate theory that eventually becomes accepted.

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This guide is licensed under the GNU Free Documentation License. It uses material from the Wikipedia.

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