Hypothesis: Wikis

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From Wikipedia, the free encyclopedia

A hypothesis (from Greek ὑπόθεσις; plural hypotheses) is a proposed explanation for an observable phenomenon. The term derives from the Greek, ὑποτιθέναι – hypotithenai meaning "to put under" or "to suppose." For a hypothesis to be put forward as a scientific hypothesis, the scientific method requires that one can test it. Scientists generally base scientific hypotheses on previous observations that cannot be satisfactorily explained with the available scientific theories. Even though the words "hypothesis" and "theory" are often used synonymously in common and informal usage, a scientific hypothesis is not the same as a scientific theory – although the difference is sometimes more one of degree than of principle.

A working hypothesis is a provisionally accepted hypothesis.

In a related but distinguishable usage, the term hypothesis is used for the antecedent of a proposition; thus in proposition "If P, then Q", P denotes the hypothesis (or antecedent); Q can be called a consequent. P is the assumption in a (possibly counterfactual) What If question.

The adjective hypothetical, meaning "having the nature of a hypothesis," or "being assumed to exist as an immediate consequence of a hypothesis," can refer to any of these meanings of the term "hypothesis."

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Uses

In Plato's Meno (86e–87b), Socrates dissects virtue with a method used by mathematicians,[1] that of "investigating from a hypothesis."[2] In this sense, 'hypothesis' refers to a clever idea or to a convenient mathematical approach that simplifies cumbersome calculations.[3] Cardinal Bellarmine gave a famous example of this usage in the warning issued to Galileo in the early 17th century: that he must not treat the motion of the Earth as a reality, but merely as a hypothesis.[4]

In common usage in the 21st century, a hypothesis refers to a provisional idea whose merit requires evaluation. For proper evaluation, the framer of a hypothesis needs to define specifics in operational terms. A hypothesis requires more work by the researcher in order to either confirm or disprove it. In due course, a confirmed hypothesis may become part of a theory or occasionally may grow to become a theory itself. Normally, scientific hypotheses have the form of a mathematical model. Sometimes, but not always, one can also formulate them as existential statements, stating that some particular instance of the phenomenon under examination has some characteristic and causal explanations, which have the general form of universal statements, stating that every instance of the phenomenon has a particular characteristic.

Any useful hypothesis will enable predictions by reasoning (including deductive reasoning). It might predict the outcome of an experiment in a laboratory setting or the observation of a phenomenon in nature. The prediction may also invoke statistics and only talk about probabilities. Karl Popper, following others, has argued that a hypothesis must be falsifiable, and that one cannot regard a proposition or theory as scientific if it does not admit the possibility of being shown false. Other philosophers of science have rejected the criterion of falsifiability or supplemented it with other criteria, such as verifiability (e.g., verificationism) or coherence (e.g., confirmation holism). The scientific method involves experimentation on the basis of hypotheses in order to answer questions and explore observations.

In framing a hypothesis, the investigator must not currently know the outcome of a test or that it remains reasonably under continuing investigation. Only in such cases does the experiment, test or study potentially increase the probability of showing the truth of a hypothesis. If the researcher already knows the outcome, it counts as a "consequence" — and the researcher should have already considered this while formulating the hypothesis. If one cannot assess the predictions by observation or by experience, the hypothesis classes as not yet useful, and must wait for others who might come afterward to make possible the needed observations. For example, a new technology or theory might make the necessary experiments feasible.

Scientific hypothesis

People refer to a trial solution to a problem as a hypothesis — often called an "educated guess"[5] — because it provides a suggested solution based on the evidence. Experimenters may test and reject several hypotheses before solving the problem.

According to Schick and Vaughn,[6] researchers weighing up alternative hypotheses may take into consideration:

  • Testability (compare falsifiability as discussed above)
  • Simplicity (as in the application of "Occam's razor", discouraging the postulation of excessive numbers of entities)
  • Scope – the apparent application of the hypothesis to multiple cases of phenomena
  • Fruitfulness – the prospect that a hypothesis may explain further phenomena in the future
  • Conservatism – the degree of "fit" with existing recognized knowledge-systems

Evaluating hypotheses

According to Karl Popper's hypothetico-deductive method (also known as the method of "conjectures and refutations") demands falsifiable hypotheses, framed in such a manner that the scientific community can prove them false (usually by observation). According to this view, a hypothesis cannot be "confirmed", because there is always the possibility that a future experiment will show that it is false. Hence, failing to falsify a hypothesis does not prove that hypothesis: it remains provisional. However, a hypothesis that has been rigorously tested and not falsified can form a reasonable basis for action, i.e., we can act as if it is true, until such time as it is falsified. Just because we've never observed rain falling upward, doesn't mean that we never will—however improbable, our theory of gravity may be falsified some day.

Popper's view is not the only view on evaluating hypotheses. For example, some forms of empiricism hold that under a well-crafted, well-controlled experiment, a lack of falsification does count as verification, since such an experiment ranges over the full scope of possibilities in the problem domain. Should we ever discover some place where gravity did not function, and rain fell upward, this would not falsify our current theory of gravity (which, on this view, has been verified by innumerable well-formed experiments in the past) – it would rather suggest an expansion of our theory to encompass some new force or previously undiscovered interaction of forces. In other words, our initial theory as it stands is verified but incomplete. This situation illustrates the importance of having well-crafted, well-controlled experiments that range over the full scope of possibilities for applying the theory.

In recent years philosophers of science have tried to integrate the various approaches to evaluating hypothesis, and the scientific method in general, to form a more complete system that integrates the individual concerns of each approach. Notably, Imre Lakatos and Paul Feyerabend, both former students of Popper, have produced novel attempts at such a synthesis.

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Statistical hypothesis testing

When a possible correlation or similar relation between phenomena is investigated, such as, for example, whether a proposed remedy is effective in treating a disease, that is, at least to some extent and for some patients, the hypothesis that a relation exists cannot be examined the same way one might examine a proposed new law of nature: in such an investigation a few cases in which the tested remedy shows no effect do not falsify the hypothesis. Instead, statistical tests are used to determine how likely it is that the overall effect would be observed if no real relation as hypothesized exists. If that likelihood is sufficiently small (e.g., less than 1%), the existence of a relation may be assumed. Otherwise, any observed effect may as well be due to pure chance.

In statistical hypothesis testing two hypotheses are compared, which are called the null hypothesis and the alternative hypothesis. The null hypothesis is the hypothesis that states that there is no relation between the phenomena whose relation is under investigation, or at least not of the form given by the alternative hypothesis. The alternative hypothesis, as the name suggests, is the alternative to the null hypothesis: it states that there is some kind of relation. The alternative hypothesis may take several forms, depending on the nature of the hypothesized relation; in particular, it can be two-sided (for example: there is some effect, in a yet unknown direction) or one-sided (the direction of the hypothesized relation, positive or negative, is fixed in advance).

Proper use of statistical testing requires that these hypotheses, and the threshold (such as 1%) at which the null hypothesis is rejected and the alternative hypothesis is accepted, all be determined in advance, before the observations are collected or inspected. If these criteria are determined later, when the data to be tested is already known, the test is invalid.

See also

References

  1. ^ Wilbur R. Knorr, "Construction as existence proof in ancient geometry", p. 125, as selected by Jean Christianidis (ed.), Classics in the history of Greek mathematics, Kluwer.
  2. ^ Gregory Vlastos, Myles Burnyeat (1994) Socratic studies, Cambridge ISBN 0521447356, p. 1
  3. ^ "Neutral hypotheses, those of which the subject matter can never be directly proved or disproved, are very numerous in all sciences." — Morris Cohen and Ernest Nagel (1934) An introduction to logic and scientific method p. 375. New York: Harcourt, Brace, and Company.
  4. ^ "Bellarmine (Ital. Bellarmino), Roberto Francesco Romolo", Encyclopædia Britannica, Eleventh Edition.: 'Bellarmine did not proscribe the Copernican system ... all he claimed was that it should be presented as an hypothesis until it should receive scientific demonstration.' This article incorporates text from the Encyclopædia Britannica, Eleventh Edition, a publication now in the public domain.
  5. ^ "When it is not clear under which law of nature an effect or class of effect belongs, we try to fill this gap by means of a guess. Such guesses have been given the name conjectures or hypotheses." — Hans Christian Ørsted(1811) "First Introduction to General Physics" ¶18. Selected Scientific Works of Hans Christian Ørsted, ISBN 0-691-04334-5 p.297
  6. ^ Schick, Theodore; Vaughn, Lewis (2002). How to think about weird things: critical thinking for a New Age. Boston: McGraw-Hill Higher Education. ISBN 0-7674-2048-9. 

Study guide

Up to date as of January 14, 2010

From Wikiversity

Tips for stating hypotheses

  1. Make hypotheses as explicit, clear, and understandable to an outside reader as possible.
  2. Break complicated hypotheses down into sub-hypotheses.
  3. Each hypothesis should be able to be one test (or series of related tests) as "yes" or "no".

See also


1911 encyclopedia

Up to date as of January 14, 2010

From LoveToKnow 1911

HYPOTHESIS (from Gr. urortO vat, to put under; cf. Lat. suppositio, from sub-ponere), in ordinary language, an explanation, supposition or assumption, which is put forward in the absence of ascertained facts or causes. Both in ordinary life and in the acquisition of scientific knowledge hypothesis is all-important. A detective's work consists largely in forming and testing hypothesis. If an astronomer is confronted by some phenomenon which has no obvious explanation he may postulate some set of conditions which from his general knowledge of the subject would or might give rise to the phenomenon in question; he then tests his hypothesis until he discovers whether it does or does not conflict with the facts. An example of this process is that of the discovery of the planet Neptune: certain perturbations of the orbit of Uranus had been observed, and it was seen that these could be explained on the hypothesis of the existence of a then unknown planet, and this hypothesis was verified by actual observation. The progress of inductive knowledge is by the formation of successive hypotheses, and it frequently happens that the demolition of one or even many hypotheses is the direct road to a new and accurate hypothesis, i.e. to fresh knowledge. A hypothesis may, therefore, turn out to be entirely wrong, yet it may be of the greatest practical use.

The recognition of the importance of hypotheses has led to various attempts at drawing up exact rules for their formation, but logicians are generally agreed that only very elementary principles can be laid down. Thus a hypothesis must contain nothing which is at variance with known facts or principles: it should not postulate conditions which cannot be verified empirically. J. S. Mill (Logic III. xiv. 4) laid down the principle that a hypothesis is not "genuinely scientific" if it is "destined always to remain a hypothesis": it must "be of such a nature as to be either proved or disproved by comparison with observed facts": in the same spirit Bacon said that in searching for causes in nature "Deum semper excipimus." Mill's principle, though sound in the abstract, has, except in a few cases, little practical value in determining the admissibility of hypotheses, and in practice any rule which tends to discourage hypothesis is in general undesirable. The most satisfactory check on hypothesis is expert knowledge in the particular field of research by which rigorous tests may be applied. This test is roughly of two kinds, first by the ultimate principles or presuppositions on which a particular branch of knowledge rests, and second by the comparison of correlative facts. Useful light is shed on this distinction by Lotze, who contrasts (Logic, § 273) postulates (" absolutely necessary assumptions without which the content of the observation with which we are dealing would contradict the laws of our thought") with hypotheses, which he defines as conjectures, which seek "to fill up the postulate thus abstractly stated by specifying the concrete causes, forces or processes, out of which the given phenomenon really arose in this particular case, while in other cases maybe the same postulate is to be satisfied by utterly different though equivalent combinations of forces or active elements." Thus a hypothesis may be ruled out by principles or postulates without any reference to the concrete facts which belong to that division of the subject to explain which the hypothesis is formulated. A true hypothesis, therefore, seeks not merely to connect or colligate two separate facts, but to do this in the light of and subject to certain fundamental principles. Various attempts have been made to classify hypotheses and to distinguish "hypothesis" from a "theory" or a mere "conjecture": none of these have any great practical importance, the differences being only in degree, not in kind.

The adjective "hypothetical" is used in the same sense, both loosely in contradistinction to "real" or "actual," and technically in the phrases "hypothetical judgment" and "hypothetical syllogism." (See LOGIC and SYLLOGISM.) See Naville, La Logique de l'hypothbse (1880), and textbooks of logic, e.g. those of Jevons, Bosanquet, Joseph; Liebmann, Der Klimax d. Theorien.


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Simple English

A hypothesis is something that can explain a event. It can propose or suggest how two events relate to each other. The term comes from the Greek, hypotithenai meaning "to put under" or "to suppose." The scientific method requires that a scientific hypothesis can be tested. Scientists sometimes create hypotheses on events that have been seen before or on extensions of scientific theories.

Contents

Usage

At first, educated people often referred to an idea or to an approach to math that made hard math easier as a hypothesis; when used this way, the word did not necessarily have any specific meaning. Cardinal Bellarmine gave a well known example of the older sense of the word in the warning issued to Galileo in the early 17th century: that he must not treat the motion of the Earth as a reality, but merely as a hypothesis.

In common usage in the 21st century, a hypothesis refers to a idea that needs to be tested. A hypothesis needs more work by the researcher in order to check it. A tested hypothesis that works, may become part of a theory or become a theory itself. Normally, scientific hypotheses have the form of a mathematical model.

Other pages

References

  • Schick, Theodore and Vaughn, Lewis: How to think about weird things: Critical thinking for a New Age Boston, 2002

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