
The scientific method is an
empirical method for acquiring
knowledge
Knowledge can be defined as awareness of facts or as practical skills, and may also refer to familiarity with objects or situations. Knowledge of facts, also called propositional knowledge, is often defined as true belief that is disti ...
that has characterized the development of
science
Science is a systematic endeavor that Scientific method, builds and organizes knowledge in the form of Testability, testable explanations and predictions about the universe.
Science may be as old as the human species, and some of the earli ...
since at least the 17th century (with notable practitioners in previous centuries; see the article
history of scientific method for additional detail.) It involves careful
observation, applying rigorous
skepticism about what is observed, given that
cognitive assumptions can distort how one interprets the
observation. It involves formulating
hypotheses, via
induction, based on such observations; the
testability of hypotheses,
experiment
An experiment is a procedure carried out to support or refute a hypothesis, or determine the efficacy or likelihood of something previously untried. Experiments provide insight into cause-and-effect by demonstrating what outcome occurs wh ...
al and the measurement-based statistical testing of
deductions drawn from the hypotheses; and refinement (or elimination) of the hypotheses based on the experimental findings. These are ''principles'' of the scientific method, as distinguished from a definitive series of steps applicable to all scientific enterprises.
Although procedures vary from one
field of inquiry to another, the underlying
process is frequently the same from one field to another. The process in the scientific method involves making
conjecture
In mathematics, a conjecture is a conclusion or a proposition that is proffered on a tentative basis without proof. Some conjectures, such as the Riemann hypothesis (still a conjecture) or Fermat's Last Theorem (a conjecture until proven in 1 ...
s (hypothetical explanations), deriving predictions from the hypotheses as logical consequences, and then carrying out experiments or empirical observations based on those predictions.
A hypothesis is a conjecture, based on knowledge obtained while seeking answers to the question. The hypothesis might be very specific, or it might be broad. Scientists then test hypotheses by conducting experiments or studies. A scientific hypothesis must be
falsifiable, implying that it is possible to identify a possible outcome of an experiment or observation that conflicts with predictions deduced from the hypothesis; otherwise, the hypothesis cannot be meaningfully tested.
The purpose of an experiment is to determine whether
observations agree with or conflict with the
expectation
Expectation or Expectations may refer to:
Science
* Expectation (epistemic)
* Expected value, in mathematical probability theory
* Expectation value (quantum mechanics)
* Expectation–maximization algorithm, in statistics
Music
* ''Expectation' ...
s deduced from a hypothesis.
[ Experiments can take place anywhere from a garage to a remote mountaintop to CERN's Large Hadron Collider. There are difficulties in a formulaic statement of method, however. Though the scientific method is often presented as a fixed sequence of steps, it represents rather a set of general principles.][: "The scientific method 'is often misrepresented as a fixed sequence of steps,' rather than being seen for what it truly is, 'a highly variable and creative process' (AAAS 2000:18). The claim here is that science has general principles that must be mastered to increase productivity and enhance perspective, not that these principles provide a simple and automated sequence of steps to follow."] Not all steps take place in every scientific inquiry (nor to the same degree), and they are not always in the same order.[ William Whewell, ''History of Inductive Science'' (1837), and in ''Philosophy of Inductive Science'' (1840)]
History
Important debates in the history of science concern skepticism that anything can be known for sure (such as views of Francisco Sanches
Francisco Sanches (also spelled Sánchez in contemporary sources; c. 1550 – November 16, 1623) was a skeptic, philosopher and physician of Sephardi Jewish origin, born in Tui, Spain (although he was baptized in Braga, Portugal).Elaine Limb ...
), rationalism (especially as advocated by René Descartes
René Descartes ( or ; ; Latinized: Renatus Cartesius; 31 March 1596 – 11 February 1650) was a French philosopher, scientist, and mathematician, widely considered a seminal figure in the emergence of modern philosophy and science. Mathe ...
), inductivism, empiricism (as argued for by Francis Bacon
Francis Bacon, 1st Viscount St Alban (; 22 January 1561 – 9 April 1626), also known as Lord Verulam, was an English philosopher and statesman who served as Attorney General and Lord Chancellor of England. Bacon led the advancement of both ...
, then rising to particular prominence with Isaac Newton
Sir Isaac Newton (25 December 1642 – 20 March 1726/27) was an English mathematician, physicist, astronomer, alchemist, theologian, and author (described in his time as a " natural philosopher"), widely recognised as one of the g ...
and his followers), and hypothetico-deductivism, which came to the fore in the early 19th century.
The term "scientific method" emerged in the 19th century, when a significant institutional development of science was taking place and terminologies establishing clear boundaries between science and non-science, such as "scientist" and "pseudoscience", appeared. Throughout the 1830s and 1850s, at which time Baconianism was popular, naturalists like William Whewell, John Herschel, John Stuart Mill engaged in debates over "induction" and "facts" and were focused on how to generate knowledge. In the late 19th and early 20th centuries, a debate over realism vs. antirealism was conducted as powerful scientific theories extended beyond the realm of the observable.
Problem-solving via scientific method
:''See Notes section § Problem-solving via scientific method''
The term "scientific method" came into popular use in the twentieth century; Dewey's 1910 book, '' How We Think'', inspired popular guidelines, popping up in dictionaries and science textbooks, although there was little consensus over its meaning. Although there was growth through the middle of the twentieth century, by the 1960s and 1970s numerous influential philosophers of science such as Thomas Kuhn
Thomas Samuel Kuhn (; July 18, 1922 – June 17, 1996) was an American philosopher of science whose 1962 book ''The Structure of Scientific Revolutions'' was influential in both academic and popular circles, introducing the term '' paradig ...
and Paul Feyerabend
Paul Karl Feyerabend (; January 13, 1924 – February 11, 1994) was an Austrian-born philosopher of science best known for his work as a professor of philosophy at the University of California, Berkeley, where he worked for three decades (195 ...
had questioned the universality of the "scientific method" and in doing so largely replaced the notion of science as a homogeneous and universal method with that of it being a heterogeneous and local practice. In particular, Paul Feyerabend, in the 1975 first edition of his book '' Against Method'', argued against there being any universal rules of science
Science is a systematic endeavor that Scientific method, builds and organizes knowledge in the form of Testability, testable explanations and predictions about the universe.
Science may be as old as the human species, and some of the earli ...
; Popper 1963,[Popper (1963) ''Conjectures and Refutations'' pp=312-365]
claims that Trial and error
Trial and error is a fundamental method of problem-solving characterized by repeated, varied attempts which are continued until success, or until the practicer stops trying.
According to W.H. Thorpe, the term was devised by C. Lloyd Morgan ( ...
is a universal method. Gauch 2003, and Tow 2010 disagree with Feyerabend's claim; problem solver
In professional wrestling double-team maneuvers are executed by multiple wrestlers instead of one and typically are used by tag teams in tag team matches. Many of these maneuvers are combination of two throws, or submission holds. Most moves are ...
s, and researchers are to be prudent with their resources during their inquiry.
Later stances include physicist Lee Smolin
Lee Smolin (; born June 6, 1955) is an American theoretical physicist, a faculty member at the Perimeter Institute for Theoretical Physics, an adjunct professor of physics at the University of Waterloo and a member of the graduate faculty of th ...
's 2013 essay "There Is No Scientific Method", in which he espouses two ethical principles, and historian of science Daniel Thurs's chapter in the 2015 book ''Newton's Apple and Other Myths about Science'', which concluded that the scientific method is a myth or, at best, an idealization. As myth
Myth is a folklore genre consisting of narratives that play a fundamental role in a society, such as foundational tales or origin myths. Since "myth" is widely used to imply that a story is not objectively true, the identification of a narrati ...
s are beliefs, they are subject to the narrative fallacy as Taleb points out. Philosophers Robert Nola
Robert Nola (25 June 1940 - 23 October 2022) was a New Zealand philosophy academic, and was an Emeritus Professor in the Department of Philosophy at the University of Auckland. His work focussed on the philosophy and history of science, on epist ...
and Howard Sankey, in their 2007 book ''Theories of Scientific Method'', said that debates over scientific method continue, and argued that Feyerabend, despite the title of ''Against Method'', accepted certain rules of method and attempted to justify those rules with a meta methodology.
Staddon (2017) argues it is a mistake to try following rules in the absence of an algorithmic scientific method; in that case, "science is best understood through examples". But algorithmic methods, such as ''disproof of existing theory by experiment'' have been used since Alhacen (1027) ''Book of Optics'', and Galileo (1638) ''Two New Sciences'', and ''The Assayer'' still stand as scientific method. They contradict Feyerabend's stance.
The ubiquitous element in the scientific method is empiricism. This is in opposition to stringent forms of rationalism: the scientific method embodies the position that reason alone cannot solve a particular scientific problem. A strong formulation of the scientific method is not always aligned with a form of empiricism in which the empirical data is put forward in the form of experience or other abstracted forms of knowledge; in current scientific practice, however, the use of scientific modelling
Scientific modelling is a scientific activity, the aim of which is to make a particular part or feature of the world easier to understand, define, quantify, visualize, or simulate by referencing it to existing and usually commonly accepted ...
and reliance on abstract typologies and theories is normally accepted. The scientific method counters claims that revelation
In religion and theology, revelation is the revealing or disclosing of some form of truth or knowledge through communication with a deity or other supernatural entity or entities.
Background
Inspiration – such as that bestowed by God on th ...
, political or religious dogma
Dogma is a belief or set of beliefs that is accepted by the members of a group without being questioned or doubted. It may be in the form of an official system of principles or doctrines of a religion, such as Roman Catholicism, Judaism, Islam ...
, appeals to tradition, commonly held beliefs, common sense, or currently held theories pose the only possible means of demonstrating truth.
Different early expressions of empiricism and the scientific method can be found throughout history, for instance with the ancient Stoics
Stoicism is a school of Hellenistic philosophy founded by Zeno of Citium in Athens in the early 3rd century BCE. It is a philosophy of personal virtue ethics informed by its system of logic and its views on the natural world, asserting th ...
, Epicurus,[Elizabeth Asmis (1985) ''Epicurus' Scientific Method''. Cornell University Press] Alhazen, Avicenna
Ibn Sina ( fa, ابن سینا; 980 – June 1037 CE), commonly known in the West as Avicenna (), was a Persian polymath who is regarded as one of the most significant physicians, astronomers, philosophers, and writers of the Islam ...
, Roger Bacon, and William of Ockham
William of Ockham, OFM (; also Occam, from la, Gulielmus Occamus; 1287 – 10 April 1347) was an English Franciscan friar, scholastic philosopher, apologist, and Catholic theologian, who is believed to have been born in Ockham, a small vi ...
. From the 16th century onwards, experiments were advocated by Francis Bacon
Francis Bacon, 1st Viscount St Alban (; 22 January 1561 – 9 April 1626), also known as Lord Verulam, was an English philosopher and statesman who served as Attorney General and Lord Chancellor of England. Bacon led the advancement of both ...
, and performed by Giambattista della Porta
Giambattista della Porta (; 1535 – 4 February 1615), also known as Giovanni Battista Della Porta, was an Italian scholar, polymath and playwright who lived in Naples at the time of the Renaissance, Scientific Revolution and Reformation.
Giamb ...
, Johannes Kepler, and Galileo Galilei
Galileo di Vincenzo Bonaiuti de' Galilei (15 February 1564 – 8 January 1642) was an Italian astronomer, physicist and engineer, sometimes described as a polymath. Commonly referred to as Galileo, his name was pronounced (, ). He w ...
. There was particular development aided by theoretical works by Francisco Sanches
Francisco Sanches (also spelled Sánchez in contemporary sources; c. 1550 – November 16, 1623) was a skeptic, philosopher and physician of Sephardi Jewish origin, born in Tui, Spain (although he was baptized in Braga, Portugal).Elaine Limb ...
, John Locke, George Berkeley
George Berkeley (; 12 March 168514 January 1753) – known as Bishop Berkeley ( Bishop of Cloyne of the Anglican Church of Ireland) – was an Anglo-Irish philosopher whose primary achievement was the advancement of a theory he called "immate ...
, and David Hume
David Hume (; born David Home; 7 May 1711 NS (26 April 1711 OS) – 25 August 1776) Cranston, Maurice, and Thomas Edmund Jessop. 2020 999br>David Hume" ''Encyclopædia Britannica''. Retrieved 18 May 2020. was a Scottish Enlightenment phil ...
.
A sea voyage from America to Europe afforded C. S. Peirce the distance to clarify his ideas, gradually resulting in the hypothetico-deductive model
The hypothetico-deductive model or method is a proposed description of the scientific method. According to it, scientific inquiry proceeds by formulating a hypothesis in a form that can be falsifiable, using a test on observable data where the o ...
. Formulated in the 20th century, the model has undergone significant revision since first proposed (for a more formal discussion, see ).
Overview
The scientific method is the process by which science
Science is a systematic endeavor that Scientific method, builds and organizes knowledge in the form of Testability, testable explanations and predictions about the universe.
Science may be as old as the human species, and some of the earli ...
is carried out.[: "The thesis of this book, as outlined in Chapter One, is that there are general principles applicable to all the sciences."] As in other areas of inquiry, science (through the scientific method) can build on previous knowledge and develop a more sophisticated understanding of its topics of study over time.Leon Lederman
Leon, Léon (French) or León (Spanish) may refer to:
Places
Europe
* León, Spain, capital city of the Province of León
* Province of León, Spain
* Kingdom of León, an independent state in the Iberian Peninsula from 910 to 1230 and again fr ...
, for teaching physics first, illustrates how to avoid confirmation bias: Ian Shelton, in Chile, was initially skeptical that supernova 1987a
SN 1987A was a type II supernova in the Large Magellanic Cloud, a dwarf satellite galaxy of the Milky Way. It occurred approximately from Earth and was the closest observed supernova since Kepler's Supernova. 1987A's light reached Earth on Febr ...
was real, but possibly an artifact of instrumentation (null hypothesis), so he went outside and disproved his null hypothesis by observing SN 1987a with the naked eye. The Kamiokande
The is a neutrino and gravitational waves laboratory located underground in the Mozumi mine of the Kamioka Mining and Smelting Co. near the Kamioka section of the city of Hida in Gifu Prefecture, Japan. A set of groundbreaking neutrino experim ...
experiment, in Japan, independently observed neutrino
A neutrino ( ; denoted by the Greek letter ) is a fermion (an elementary particle with spin of ) that interacts only via the weak interaction and gravity. The neutrino is so named because it is electrically neutral and because its rest mass ...
s from SN 1987a at the same time.[ This model can be seen to underlie the ]scientific revolution
The Scientific Revolution was a series of events that marked the emergence of modern science during the early modern period, when developments in mathematics, physics, astronomy, biology (including human anatomy) and chemistry transformed ...
.[: "There is a danger that must be avoided. ... If we wish to do justice to the historical enterprise, we must take the past for what it was. And that means we must resist the temptation to scour the past for examples or precursors of modern science. ...My concern will be with the beginnings of scientific ''theories'', the methods by which they were formulated, and the uses to which they were put; ... "]
Process
The overall process involves making conjecture
In mathematics, a conjecture is a conclusion or a proposition that is proffered on a tentative basis without proof. Some conjectures, such as the Riemann hypothesis (still a conjecture) or Fermat's Last Theorem (a conjecture until proven in 1 ...
s ( hypotheses), deriving predictions from them as logical consequences, and then carrying out experiments based on those predictions to determine whether the original conjecture was correct. There are difficulties in a formulaic statement of method, however. Though the scientific method is often presented as a fixed sequence of steps, these actions are better considered as general principles. Not all steps take place in every scientific inquiry (nor to the same degree), and they are not always done in the same order. As noted by scientist and philosopher William Whewell (1794–1866), "invention, sagacity, ndgenius" are required at every step.
Formulation of a question
The question can refer to the explanation of a specific observation, as in "Why is the sky blue?" but can also be open-ended, as in "How can I design a drug to cure this particular disease?" This stage frequently involves finding and evaluating evidence from previous experiments, personal scientific observations or assertions, as well as the work of other scientists. If the answer is already known, a different question that builds on the evidence can be posed. When applying the scientific method to research, determining a good question can be very difficult and it will affect the outcome of the investigation.
Hypothesis
A hypothesis
A hypothesis (plural hypotheses) is a proposed explanation for a phenomenon. For a hypothesis to be a scientific hypothesis, the scientific method requires that one can testable, test it. Scientists generally base scientific hypotheses on prev ...
is a conjecture, based on knowledge obtained while formulating the question, that may explain any given behavior. The hypothesis might be very specific; for example, Einstein's equivalence principle or Francis Crick
Francis Harry Compton Crick (8 June 1916 – 28 July 2004) was an English molecular biologist, biophysicist, and neuroscientist. He, James Watson, Rosalind Franklin, and Maurice Wilkins played crucial roles in deciphering the helical stru ...
's "DNA makes RNA makes protein", or it might be broad; for example, "unknown species of life dwell in the unexplored depths of the oceans". ''See § Hypothesis development''
A statistical hypothesis
A statistical hypothesis test is a method of statistical inference used to decide whether the data at hand sufficiently support a particular hypothesis.
Hypothesis testing allows us to make probabilistic statements about population parameters.
...
is a conjecture
In mathematics, a conjecture is a conclusion or a proposition that is proffered on a tentative basis without proof. Some conjectures, such as the Riemann hypothesis (still a conjecture) or Fermat's Last Theorem (a conjecture until proven in 1 ...
about a given statistical population
In statistics, a population is a set of similar items or events which is of interest for some question or experiment. A statistical population can be a group of existing objects (e.g. the set of all stars within the Milky Way galaxy) or a hypot ...
. For example, the population might be ''people with a particular disease''. One conjecture might be that a new drug will cure the disease in some of the people in that population, as in a clinical trial
Clinical trials are prospective biomedical or behavioral research studies on human subject research, human participants designed to answer specific questions about biomedical or behavioral interventions, including new treatments (such as novel v ...
of the drug.Bill and Melinda Gates Foundation
The Bill & Melinda Gates Foundation (BMGF), a merging of the William H. Gates Foundation and the Gates Learning Foundation, is an American private foundation founded by Bill Gates and Melinda French Gates. Based in Seattle, Washington, it was ...
A null hypothesis
In scientific research, the null hypothesis (often denoted ''H''0) is the claim that no difference or relationship exists between two sets of data or variables being analyzed. The null hypothesis is that any experimentally observed difference is d ...
would conjecture that the statistical hypothesis is false; for example, that the new drug does nothing, and that any cure in the population would be caused by chance (a random variable
A random variable (also called random quantity, aleatory variable, or stochastic variable) is a mathematical formalization of a quantity or object which depends on random events. It is a mapping or a function from possible outcomes (e.g., the p ...
).
An alternative to the null hypothesis, to be falsifiable, must say that a treatment program with the drug does better than chance. To test the statement ''a treatment program with the drug does better than chance'', an experiment is designed in which a portion of the population (the control group), is to be left untreated, while another, separate portion of the population is to be treated. t-Test
A ''t''-test is any statistical hypothesis test in which the test statistic follows a Student's ''t''-distribution under the null hypothesis. It is most commonly applied when the test statistic would follow a normal distribution if the value of a ...
s could then specify how large the treated groups, and how large the control groups are to be, in order to infer whether some course of treatment of the population has resulted in a cure of some of them, in each of the groups. The groups are examined, in turn by the researchers, in a protocol.
Strong inference
In philosophy of science, strong inference is a model of scientific inquiry that emphasizes the need for alternative hypotheses, rather than a single hypothesis to avoid confirmation bias.
The term "strong inference" was coined by John R. Pla ...
could alternatively propose multiple alternative hypotheses embodied in randomized controlled trial
A randomized controlled trial (or randomized control trial; RCT) is a form of scientific experiment used to control factors not under direct experimental control. Examples of RCTs are clinical trials that compare the effects of drugs, surgical ...
s, treatments A, B, C, ... , (say in a blinded experiment
In a blind or blinded experiment, information which may influence the participants of the experiment is withheld until after the experiment is complete. Good blinding can reduce or eliminate experimental biases that arise from a participants' exp ...
with varying dosages, or with lifestyle changes, and so forth) so as not to introduce confirmation bias
Confirmation bias is the tendency to search for, interpret, favor, and recall information in a way that confirms or supports one's prior beliefs or values. People display this bias when they select information that supports their views, ignorin ...
in favor of a specific course of treatment. Ethical considerations could be used, to minimize the numbers in the untreated groups, e.g., use almost every treatment in every group, but excluding A, B, C, ..., respectively as controls.
Prediction
The prediction step deduces the logical consequences of the hypothesis ''before the outcome is known''. These predictions are expectations for the results of testing. If the result is already known, it is evidence that is ready to be considered in acceptance or rejection of the hypothesis.
The evidence is also stronger if the actual result of the predictive test is not already known, as tampering with the test can be ruled out, as can hindsight bias (see postdiction
Postdiction involves explanation after the fact.
In skepticism, it is considered an effect of hindsight bias that explains claimed predictions of significant events such as plane crashes and natural disasters. In religious contexts, theologian ...
). Ideally, the prediction must also distinguish the hypothesis from likely alternatives; if two hypotheses make the same prediction, observing the prediction to be correct is not evidence for either one over the other. (These statements about the relative strength of evidence can be mathematically derived using Bayes' Theorem
In probability theory and statistics, Bayes' theorem (alternatively Bayes' law or Bayes' rule), named after Thomas Bayes, describes the probability of an event, based on prior knowledge of conditions that might be related to the event. For exa ...
).
The consequence, therefore, is to be stated at the same time or briefly after the statement of the hypothesis, but before the experimental result is known.
Likewise, the test protocol is to be stated before execution of the test. These requirements become precautions against tampering, and aid the reproducibility of the experiment.
Testing
Suitable tests[ of a hypothesis compare the ]expected value
In probability theory, the expected value (also called expectation, expectancy, mathematical expectation, mean, average, or first moment) is a generalization of the weighted average. Informally, the expected value is the arithmetic mean of a ...
s from the tests of that hypothesis with the actual results of those tests. Scientists (and other people) can then secure, or discard, their hypotheses by conducting suitable experiment
An experiment is a procedure carried out to support or refute a hypothesis, or determine the efficacy or likelihood of something previously untried. Experiments provide insight into cause-and-effect by demonstrating what outcome occurs wh ...
s.
Analysis
An analysis determines, from the results of the experiment, the next actions to take. The expected values from the test of the alternative hypothesis are compared to the