Project Outline

Collect the top (maximum 100) definitions of science as it is defined by famous scientists and philosophers from the time of Aristotle, Newton, Descartes up to modern scientists like Einstein and contemporary philosophers such as Russell, Whitehead, Karl Popper, Toulmin, Hawking, etc.

The purpose is not to find out how each scientist defined it, but to find out how the conception of science has evolved over time and how many different definitions or conceptions exist today.

We are not interested in the history of science or descriptions of scientific activities or methodologies or examples, simply in how scientists and philosophers have defined the discipline and concept of science. What constitutes science and what does not and why?

Research Information

Definitions of Science

Any strict definition of science seems to be inadequate. The word "science" came from the Latin word for knowledge: scientia. The word 'science' comes from a Latin word 'scientia' and originally meant 'knowledge'. But it was used more particularly to stand for 'systematic knowledge' rather than just any kind of knowledge.

The baseline definition of "science," then, is human knowledge.

From the 1200's to until the 1840's science was known as natural philosophy

The philosopher Martin Heidegger correctly observed that there is no etymological link between the terms 'technology' and 'science'. The 'techn' in 'technology' and 'technique' is the Greek for 'art' (as in 'artful'), and 'art' is the Latin for 'skill'. The early Greek pioneers of science insisted on the careful distinction between 'techne' (= traditional practical know-how) and 'episteme' (= scientific knowledge), which the speakers of Latin later called 'scientia', and which the speakers of English today call 'science'.

Ancient India

While it may surprise some to think of religious sages as mundane scientists, the Indian view is that religion (universal) and science are but two sides of the same coin - in short…semantics. Whether one calls a natural phenomena wind or the wind god - Vayu - one is speaking of the same thing. Yet it seems that having a spiritual foundation not only brought out important discoveries still in use today, but these discoveries also were helpful without causing harm or destruction - Swami Sada Shiva Tirtha

Spirituality gives helpful direction and science brings speed

The meaning of the term 'science' as it is used in the context of Yoga is specific and precise as well as broad and general. Specifically it means, simply, that Yoga is not a doctrine or set of speculative beliefs but rather an objective technique for training the body and mind so as to comprehend ultimate reality. More generally however, ..., the term 'science' refers to the very precise, modern methods of experimentation, verification, and rational positivist investigation.

Yoga in Modern India: The Body Between Science and Philosophy - By Jo-seph S. Alter

Plato: (Plato around 400 BC)

Plato classified as knowledge only those things that are true all of the time; any "knowl-edge" we have that is true only some of the time, he called "opinion."

Plato drew a sharp distinction between knowledge, which is certain, and mere opinion, which is not certain.

Aristotle’s Metaphysiscs: (Aristotle around 350 BC)

Aristotle himself described his subject matter in a variety of ways: as ‘first philosophy’, or ‘the study of being qua being’, or ‘wisdom’, or ‘theology’. First philosophy is not the only field of inquiry to study beings. Natural science and mathematics also study beings, but in different ways, under different aspects. The natural scientist studies them as things that are subject to the laws of nature, as things that move and undergo change. That is, the natural scientist studies things qua movable (i.e., in so far as they are subject to change). The mathematician studies things qua countable and measurable. The metaphysician, on the other hand, studies them in a more general and abstract way — qua beings. So first phi-losophy studies the causes and principles of beings qua beings.

In Book E, Aristotle adds another description to the study of the causes and principles of beings qua beings. Whereas natural science studies objects that are material and subject to change, and mathematics studies objects that although not subject to change are nevertheless not separate from (i.e., independent of) matter, there is still room for a science that studies things (if indeed there are any) that are eternal, not subject to change, and inde-pendent of matter. Such a science, he says, is theology, and this is the “first” and “high-est” science.

Aristotle, on the other hand, believed that knowledge existed on a continuum. Some things, because they're simple and only have a limited number of causes, are true all of the time. Such things are mathematics and logic. Some things, because they have a number of causes, are true only some of the time. This includes physics, biology, ethics, politics, lit-erary knowledge and so on. He called this latter category, "probable knowledge." This dis-tinction would form the backbone of Western views of knowledge to this very day.

For Aristotle, knowledge existed on a continuum. At one end were things which were true all the time (mathematics). Moving further along the continuum were things which have a number of causes and that were true (biology). Finally, at the other end, were things which were only opinion (politics). Aristotle's concepts formed the backbone of Western ideas on knowledge.

... science does not relate exclusively to the immutable and necessary, but also to that which ordinarily happens..... Science is only a science of that which is presented to it, of that which is, or of the knowable; consequently the notion of science is clearly relative.

The History of Ancient Philosophy by Heinrich Ritter, Alexander James Wil-liam Morrison

...Science, which is formed by the discursive faculty of human mind...

The British Critic: A New Review (1796)

Archimedes (287 BC – 212 BC)

Brian Clegg: “I have my doubts about Archimedes ( first scientist...). Although he was a great mathematician and engineer, he still had the ancient Greek tendency to ignore ex-periment and rely on pure argument.”

Islamic civilization (8th - 15th Centuries)

Ibn al-Haytham developed rigorous experimental methods of controlled scientific testing in order to verify theoretical hypotheses and substantiate inductive conjectures. Ibn al-Haytham's scientific method was very similar to the modern scientific method and consisted of the following procedures:

  1. Observation
  2. Statement of problem
  3. Formulation of hypotheses
  4. Testing of hypothesis using experimentation
  5. Analysis of experimental results
  6. Interpretation of data and formulation of conclusion
  7. Publication of findings

The development of the scientific method is considered to be so fundamental to modern science that some — especially philosophers of science and practicing scientists — consider earlier inquiries into nature to be pre-scientific. Some have described Ibn al-Haytham as the "first scientist" for this reason.

"The debt of our science to that of the Arabs does not consist in startling discoveries or revolutionary theories; science owes a great deal more to Arab culture, it owes its existence. The ancient world was, as we saw, pre- scientific. The astronomy and mathematics of the Greeks were a foreign importation never thoroughly acclimatized in Greek culture. The Greeks systematized, generalized and theorized, but the patient ways of investigation, the accumulation of positive knowledge, the minute methods of science, detailed and pro-longed observation, experimental inquiry, were altogether alien to the Greek tempera-ment. [...]

What we call science arose in Europe as a result of a new spirit of inquiry, of new methods of investigation, of the method of experiment, observation, measurement, of the development of mathematics in a form unknown to the Greeks. That spirit and those methods were introduced into the European world by the Arabs." - Robert Briffault wrote in The Making of Humanity

Roger Bacon’s Opus maius: (Roger Bacon around 1250 AD)

On the instruction of the Pope, June 22, 1266, Bacon quickly wrote “an introductory work,” the Opus maius and the related works Opus minus and Opus tertium. He set out his own new model for a system of philosophical studies that would incorporate language studies and science studies then unavailable at the Universities. He succeeded in setting out a model of an experimental science on the basis of his study of Optics (Perspectiva). He does this in a new context: the application of linguistic and scientific knowledge for a better understanding of Theology and in the service of the Res publica Christiana. It would appear that Bacon was condemned by his Order in 1278 “on account of certain suspected novel-ties.” This may have been due to his interests in astrology and alchemy. –

At the beginning of the Opus maius and related works, Bacon offers a structural critique of the scholastic practice in the universities. He favors both language study and science over “Sentence-Method” as a way of interpreting the texts of Scripture. And he advocates training in mathematics and the sciences as requirements for students in theology.

The overall division of the Opus maius is Stoic: language study, natural philoso-phy/mathematics, morals. It is also clear that Bacon is constructing a “new model” for me-dieval philosophy, one in which Aristotelian concerns are taken up and transcended in a Neo-Platonism adapted towards Moral Philosophy and Christian Theology. Metaphysics is subordinated to Moral Philosophy. The latter becomes the end or finis of linguistic and sci-entific study. Logic is reduced to Mathematics, and the applications of mathematics be-come central to an understanding of the sciences.

Brian Clegg, “Some have disagreed about Bacon ( first scientist..), because he was loose in his definition of experiment, including little more than ‘someone saw X’ as well as more formal experiments.”

Brian Clegg, “Yet his biggest contribution was to link science and experiment, to insist that a study of the natural world by observation and exact measurement was the surest founda-tion for truth.”

Galileo (1564 - 1642)

He (Dr Gerald Holton) added that Galileo ... had "a wonderful way" of separating the super-natural from the natural. There are two equally worthy ways to understand the divine, Galileo said. "One was reverent contemplation of the Bible, God's word," Dr. Holton said. "The other was through scientific contemplation of the world, which is his creation.

Descartes: (1637)

Descartes started his line of reasoning by doubting everything, so as to assess the world from a fresh perspective, clear of any preconceived notions.

The first was never to accept anything for true which I did not clearly know to be such;

The second, to divide each of the difficulties under examination into as many parts as possible,

The third, to conduct my thoughts in such order that, by commencing with objects the sim-plest and easiest to know, I might ascend by little and little, and, as it were, step by step, to the knowledge of the more complex;

And the last, in every case to make enumerations so complete, and reviews so general, that I might be assured that nothing was omitted."

Isaac Newton (1642 – 1727)

Newton defined Newtonist Scholasticism as science and Peripatetic Philosophy as scholasticism.

Newton found science a hodgepodge of isolated facts and laws, capable of describing some phenomena, but predicting only a few. He left it with a unified system of laws that can be applied to an enormous range of physical phenomena, and that can be used to make exact predications.

Newton called his theory of motion 'natural philosophy' and not 'science'

John Locke (1704)

Locke defines knowledge as "the perception of the connexion and agreement, or disagree-ment and repugnancy of any of our ideas." (IV.i.2). Because it has only to do with internal relations that hold between ideas, knowledge is not actually of the world itself.

Locke identifies four different sorts of agreement and disagreement that reason can perceive in order to produce knowledge: identity and diversity (e.g. A=A); relation (e.g. a diamond is a square laid on its side); coexistence (e.g. that the area of a triangle always equals one half the base time the height); realizing that existence belongs to the very ideas themselves (e.g. the idea of God and of the self).

To count as knowledge, the connection between ideas must be very strong. In the case of disagreement, the connection must be one of logical inconsistency, and in the case of agreement, it needs to be a necessary connection. For example, in order to know that A caused B you need to know that given A, B could not have failed to happen. In other words, to know that A caused B, you need to be able to deduce B given only the information that A, or derive B from A.

Locke's definition of knowledge was common among 17th century thinkers. Both Rene Des-cartes and David Hume defined knowledge in much the same way.

19th century

And that this is what the author means, in fact, is shown expressly by his definition, which describes philosophy as pursuing the origin, the end and the essence of the facts of science.

Methodist Quarterly review 1854

...consider science as a process of questioning and answering.

Science, by American Association for the Advancement of Science

Science has been defined in terms of method of inquiry and testing. At first sight this definition may seem opposed t the current cnception that science is organized or systemaied knowledge. The opposition , however, is only seeming, and disappears when the ordinary definition is completed. Not organization but the kind of organization effected by adequate ethods of tested discovery marks off science.

Democracy and Education By John Dewey

Science is nature seen by the reason, and not merely by the senses. Science exists in the mind, and in the mind alone. Wherever the substantiveness of a science may be derived from, or whatever may be their character, they are portions of a science only as they are made to function logically in the human reason. Unless they ate connected by the law of reason, and consequent so that one proposition is capable of being correctly evolved from two or more propositions, called the premises, the science as yet has no existence, and has still to be discovered. Logic, therefore, is the universal form of all science.

The Journal of Sacred Literature By John Kitto, Henry Burgess, Benjamin Harris Cowper (1851)

Science is systematized truth.

American Education: Its Principles and Elements : Dedicated to the Teach-ers ...By Edward Deering Mansfield (1851)

William Dilthey: (1890s)

He argued that natural sciences were based on demonstration and experiment; they yielded more or less certain and reproducible knowledge. The human sciences, however, were based primarily on interpretation, that is, human knowledge of all things human, is a com-bination of experience and the human imagination operating on that experience. That was why the human sciences were so uncertain. While one could postulate rules for interpreta-tion, there was ample room for each individual to arrive at different conclusions regarding the same experience.

Ernst Mach (1838 - 1916)

All of science was or should be nothing more than compact summaries of experience

Albert Einstein (1879 - 1955)

Science without religion is lame, religion without science is blind.

He proclaimed that concepts and theories are "free inventions of the human spirit" and that no method could assuredly take us from experience to the true theory. ...... he concluded that the right concepts and theories could be found merely by seeking the mathematically simplest theories.

Einstein's notion ... concepts and theories are free inventions not fixed by experience

This sense of the closeness of theory to experience was shattered by Einstein's general the-ory of relativity. It required a new and complicated mathematics then unfamiliar to most physicists. Yet most of its predictions were no different than those of Newton's much simpler theory. If theories were merely summaries of experience and did not add to them, how could two theories, so much in agreement on experience, differ so much in structure?

Einstein's physics and the new physics developed by others in the twentieth century led to a sense of the fragility of theories and the powerlessness of evidence to pick out the unique truths of nature. Philosophers of science struggled to accommodate this new sense within their systems, all the while seeking to fit their ideas with Einstein's theories.

Michael Atiyah (1960s)

Atiyah asserted that "independence of thought really is the hallmark of a scientist".

Karl Popper (1966) (1902 – 1994)

Karl Popper, "Science is a history of corrected mistakes"

In Popper's view all the great theories of the past, such as Newtonian mechanics, are still scientific even though they have been shown to be false.

They exposed themselves to test (i.e., falsification); that is the mark of the scientific. Alas, they did not pass some of their tests and so were shown to be false.

The second way of being systematic concerns the organization of a body of knowledge into:

(a) The definition of all its fundamental concepts,
(b) The separation of all of its claims into
(b1) the fundamental laws, principles or axioms of the subject matter, and
(b2) the derivative or less fundamental laws or theorems,
(c) The vast number of observational facts that concern science, such as all the facts that one can observe and measure about bodies in motion, or their heat properties, and the like.

(Newton presented his theory of motion in this way when he published his path-breaking book Principia Mathematica first in 1686)

A scientific statement, he said, is one that can be proved wrong, like "the sun always rises in the east" or "light in a vacuum travels 186,000 miles a second." By Popper's rules, a law of science can never be proved; it can only be used to make a prediction that can be tested, with the possibility of being proved wrong.

By Popper's rules, a law of science can never be proved; it can only be used to make a pre-diction that can be tested, with the possibility of being proved wrong

Moreover, the natural sciences with their critical methods of problem solving, and some of the social sciences too, especially history and economics, have represented for quite a long time our best efforts in problem solving and fact finding (by fact finding I mean, of course, the discovery of statements or theories which correspond to facts). Thus these sciences contain, by and large, the best statements and theories from the point of view of truth; that is, those giving the best description of the world of facts, or of what one calls 'reality'.

Paul Feyerabend(1975) (1924 - 1994)

Feyerabend's position is generally seen as radical in the philosophy of science, because it implies that philosophy can neither succeed in providing a general description of science, nor in devising a method for differentiating products of science from non-scientific entities like myths.

Feyerabend's position is generally seen as radical in the philosophy of science, because it implies that philosophy can neither succeed in providing a general description of science, nor in devising a method for differentiating products of science from non-scientific entities like myths.

Thus science is much closer to myth than a scientific philosophy is prepared to admit. It is one of the many forms of thought that have been developed by man, and not necessarily the best. It is conspicuous, noisy, and impudent, but it is inherently superior only for those who have already decided in favor of a certain ideology, or who have accepted it without having ever examined its advantages and its limits. And as the accepting and rejecting of ideologies should be left to the individual it follows that the separation of state and church must be supplemented by the separation of state and science, that most recent, most ag-gressive, and most dogmatic religious institution. Such a separation may be our only chance to achieve a humanity we are capable of, but have never fully realized.

Willard Quine (1951)

The unit of empirical significance is the whole of science.

As an empiricist I continue to think of the conceptual scheme of science as a tool, ulti-mately, for predicting future experience in the light of past experience.

Science is a continuation of common sense, and it continues the common-sense expedient of swelling ontology to simplify theory.

C Marchetti (1980s)

In one of his delightfully witty essays, entitled, “On Progress and Providence”, the Italian scientist, C Marchetti, proposes a new definition of science: “the exploration of the exter-nal word by an information system through mutation and selection.” ... The same definition naturally covers technology.

The Network Revolution: Confessions of a Computer Scientist By Jacques Vallee

Stephen Hawking (1942 - )

Any sound scientific theory, whether of time or of any other concept, should in my opinion be based on the most workable philosophy of science:

Stephen Hawking, The Universe In a Nutshell p31

Alex Rosenberg (2000)

Science does not accept as knowledge what cannot be somehow subject to the test of ex-perience. But at the same time, the obligation of science to explain our experience re-quires that it go beyond and beneath that experience in the things, properties, processes and events it appeals to in providing these explanations. How to reconcile the demands of empiricism and explanation is the hardest problem for the philosophy of science, indeed, for philosophy as a whole. For if we cannot reconcile explanation and empiricism, it is pretty clear that it is empiricism that must be given up. ... But if scientific knowledge is derived not from experiment and observation, but, say, rational reflection alone, then who is to say that alternative world-views, myths, revealed religion, which claim to compete with science to explain reality will not also claim to be justified in the same way?"

Alex Rosenberg, Philosophy of Science: A Contemporary Introduction

Douglas Allchin (2000)

"Cherish mistakes, since to err is science"

SCIENCE is a self-correcting process.

Theo Theocharis (2000)

Science is an open-ended quest for knowledge, it must be clarified that it is the horizons that are constantly and ceaselessly expanded, not that one never attains any definite and final article of knowledge. The open-endedness is in the quest, not in the specific findings resulting from the quest. The quest for knowledge is open-ended because the number of individual items of possible knowledge is infinite, but each item of course is in principle fully attainable and conclusively verifiable

The current (post-)modernist (mis-)conception of science implies that science goes on for ever not because the number of truths is infinite (for allegedly there aren't any truths at all) but because science never gets anywhere.

Science is the systematic study of observational data in order to gain an understanding of the world around us. The understanding is (almost universally) supposed to somehow come about by devising models or theories that work; all that is required from a scientific theory in this scheme is empirical 'adequacy' and practical 'reliability'. Models in this scheme are mere tools that serve as instruments for routine computations and standard predictions.

science is only one of many ways of producing 'truth'; only very few insist that it is the most reliable way. It will be argued here that in fact only the scientific method (and only when correctly applied) can generate truth.

Conversely, apart from the obvious, the only truth possible is by definition scientific.

science is the one and only DEFINING characteristic of MODERN society. If one wants to really understand modern society, one will first have to understand science.

The fashionable view in recent decades has been that ALL scientific knowledge is imperma-nent and transitory.

Science is the conscious, disciplined, systematic, and sustained, endeavor to methodically discover the non-obvious truths - of both nature and society.

Another instructive lesson that one must learn from the long history of science is that theo-rizing must be securely grounded on the solid foundation of careful observation and sound logic.

The most basic hallmark of science must be CORRECTNESS of thought, expression, and exe-cution. Apart from accidental discoveries that can be made by anybody, it is 'EPISTEMO-LOGICAL CORRECTNESS' that CAUSES discovery, invention, and advancement. Freedom merely FACILITATES the communication and dissemination of discovery and invention (and, naturally, of everything else)

The American Heritage Dictionary of the English Lan-guage, Fourth Edition 2000

"The observation, identification, description, experimental investigation [scientific method], and theoretical explanation of phenomena. Such activities restricted to a class of natural phenomena. Such activities applied to an object of inquiry or study."

Kansas Science Standards. Kansas State Board of Edu-cation. Adopted February 14, 2001

Science is the human activity of seeking natural explanations for what we observe in the world around us.

Mariano Artigas (2001) (1938 - 2006)

Empirical Science is a "state of affairs," a goal-directed human activity whose existence and progress are necessarily grounded on some assumptions about the natural order and about our ability to know it. The general presuppositions of science can be considered necessary conditions of science; natural order, human cognitive ability, and science as a goal-directed enterprise are "state of affairs" tat exist in nature, in the human being, and in society, re-spectively.

The Mind of the Universe: Understanding Science and Religion - By Mariano Artigas

Kansas State Board of Education (2005)

...calls science "a systematic method of continuing investigation that uses observation, hy-pothesis testing, measurement, experimentation, logical argument and theory building to lead to more adequate explanations of natural phenomena."

John Timmer (2007)

"[Science's] conclusions are tentative, i.e., are not necessarily the final word." In this con-text, tentative should be viewed as an indication that the models and theories used to di-rect and interpret scientific research may be incomplete, inexact, or, in some cases, simply wrong. In this sense, tentativeness in science is a form of decisiveness, as it allows research to move forward despite constant uncertainty.

In this capacity, tentativeness can also play a role in the demarcation between science and non-science. Many forms of pseudoscience, such as creationism, strive to squeeze data into support of a pre-ordained and invariant conclusion. Others, such as belief in UFO abduc-tions, persist despite extensive counter evidence.

In light of this, one potential way to gain a sense of how scientific a concept is would be to ask one of its proponents what pieces of data would cause them to modify or discard their favored model.

Reliance on natural law is central to the legal definition of science in the US

It is clear that much of science is performed in reference to natural law, or involves at-tempts to describe such laws via observations of natural systems. More commonly, how-ever, natural laws act as limitations on what science will consider: models and hypotheses are formulated in reference to natural laws in the sense that nothing is proposed that knowingly violates them, and those proposals that do are rejected.

It is equally clear, however, that much of science, as well as the applied fields derived from it, occurs at a significant distance from the most fundamental of natural laws, such as those of quantum mechanics. Science has coped with this in a variety of ways. In some of these cases, observations have led to other natural laws that are separated from those of physics (for example: all organisms on earth are related through common descent). In other fields, science is still awaiting the technological advances that can allow a more direct, quantitative study of processes that can link observations to natural laws. In cases such as these, the work focuses on a subset or approximation of natural laws. For example, those studying protein structures recognize that they ultimately form through processes that originate at the quantum level. Most of the insights in the field, however, can be derived by a focus on charge attraction/repulsion and Van der Waals forces.

Because of this important position, a significant aspect of evaluating the quality of science involves judging whether the use of natural laws is appropriate. Is the observational data that supports the existence of a natural law of sufficient quality to consider that law a valid basis for scientific thought? Do the approximations chosen in a study still reflect appropri-ate physical limitations? Even though some of those who responded did not recognize the term "natural law", it is clear that these sorts of evaluations play a major role in the evaluation of the scientific literature.

In this formulation, natural laws do serve as a powerful demarcation test between science and the non-scientific.

Jim Newton (2007)

In science, the term natural science refers to a rational approach to the study of the uni-verse, which is understood as obeying rules or laws of natural origin. The term natural science is also used to distinguish those fields that use the scientific method to study nature from the social sciences, which use the scientific method to study human behavior and society, and from the formal sciences, such as mathematics and logic, which use a different methodology.

Natural sciences form the basis for the applied sciences. Together, the natural and applied sciences are distinguished from the social sciences on the one hand, and from the humanities, theology and the arts on the other. Mathematics, statistics and computer science are not considered natural sciences, but provide many tools and frameworks used within the natural sciences. Alongside this traditional usage, the phrase natural sciences is also sometimes used more narrowly to refer to its everyday usage, that is, related to natural history. In this sense "natural sciences" may refer to the biological sciences and perhaps also the earth sciences, as distinguished from the physical sciences, including astronomy, physics, and chemistry. Within the natural sciences, the term hard science is sometimes used to describe those sub-fields that rely on experimental, quantifiable data or the scientific method and focus on accuracy and objectivity. These usually include physics, chemistry and many of the sub-fields of biology. By contrast, soft science is often used to describe the scientific fields that are more reliant on qualitative research, including the social sciences

Normdoering (2007)

Science is knowledge gained by testing ideas against reality

Bruce Railsback ()

Science is the concerted human effort to understand, or to understand better, the history of the natural world and how the natural world works, with observable physical evidence as the basis of that understanding - definition by Bruce Railsback, Geology Faculty, University of Georgia

The critical commonality is that all these people are making and recording observations of nature, or of simulations of nature, in order to learn more about how nature, in the broad-est sense, works

One of their main goals is to show that old ideas (the ideas of scientists a century ago or perhaps just a year ago) are wrong and that, instead, new ideas may better explain nature

Frank Wolf ()

The scientific method has four steps

  1. Observation and description of a phenomenon or group of phenomena.
  2. Formulation of an hypothesis to explain the phenomena. In physics, the hypothesis often takes the form of a causal mechanism or a mathematical relation.
  3. Use of the hypothesis to predict the existence of other phenomena, or to predict quanti-tatively the results of new observations.
  4. Performance of experimental tests of the predictions by several independent experi-menters and properly performed experiments.

If the experiments bear out the hypothesis it may come to be regarded as a theory or law of nature (more on the concepts of hypothesis, model, theory and law below). If the experiments do not bear out the hypothesis, it must be rejected or modified. What is key in the description of the scientific method just given is the predictive power (the ability to get more out of the theory than you put in; see Barrow, 1991) of the hypothesis or theory, as tested by experiment. It is often said in science that theories can never be proved, only disproved. There is always the possibility that a new observation or a new experiment will conflict with a long-standing theory.