Hypothesis

A hypothesis is a suggested explanation of a phenomenon or reasoned proposal suggesting a possible correlation between multiple phenomena. The term derives from the ancient Greek, hypotithenai meaning "to put under" or "to suppose". The scientific method requires that one can test a scientific hypothesis. Scientists generally base such hypotheses on previous observations or on extensions of scientific theories.

Usage

In early usage, scholars often referred to a clever idea or to a convenient mathematical approach that simplified cumbersome calculations as a hypothesis; when used this way, the word did not necessarily have any specific meaning. Cardinal Bellarmine gave a famous 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 provisional idea whose merit needs 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 being studied 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 a proposition or theory cannot be called scientific if it does not admit the possibility of being shown false. By this additional criterion, it must at least in principle be possible to make an observation that would disprove the proposition as false, even if one has not actually (yet) made that observation. A falsifiable hypothesis can greatly simplify the process of testing to determine whether the hypothesis has instances in which it is false.

It is essential that the outcome be currently unknown or reasonably under continuing investigation. Only in this case does the experiment, test or study potentially increase the probability of showing the truth of an hypothesis. If the researcher already knows the outcome, it is called a consequence — and the researcher should have already considered this while formulating the hypothesis. If the predictions are not assessable by observation or by experience, the hypothesis is 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.

Types of hypothesis

Propositions may come in the form of an assertion of a correlation between, or among, two or more things, but without necessarily asserting a cause-and-effect relationship; for example: "When A changes, so does B." Or, a proposition may take the form of asserting a causal relationship (such as "A causes B"). An example of a proposition that often but not necessarily involves an assertion of causation is: If a particular independent variable is changed there also a change in a certain dependent variable. This is also known as an "If and Then" statement, whether or not it asserts a direct cause-and-effect relationship.

A hypothesis about possible correlation does not stipulate the cause and effect per se, only stating that 'A is related to B'. Causal relationships can be more difficult to verify than correlations, because quite commonly intervening variables are also involved which may give rise to the appearance of a possibly direct cause-and-effect relationship, but which upon further investigation turn out to be more directly caused by some other factor not mentioned in the proposition. Also, a mere observation of a change in one variable, when correlated with a change in another variable, can actually mistake the effect for the cause, and vice-versa (i.e., potentially get the hypothesized cause and effect backwards).

Empirical hypotheses that experimenters have repeatedly verified may become sufficiently dependable that, at some point in time, they become considered as "proven". Scientists then term such hypotheses "laws". Alternately, researchers may instead refer to such repeatedly verified hypotheses simply as "adequately verified", or "dependable".

Evaluating hypotheses

The hypothetico-deductive method demands falsifiable hypotheses, framed in such a manner that the scientific community can prove them false (usually by observation). (Note that, if confirmed, the hypothesis is not necessarily proven, but remains provisional.)

As an example: someone who enters a new country and observes only white sheep might form the hypothesis that all sheep in that country are white. It can be considered a hypothesis, as it is falsifiable. Anyone could falsify the hypothesis by observing a single black sheep. Provided that the experimental uncertainties are small (for example, provided that one can fairly reliably distinguish the observed black sheep from (say) a goat), and provided that the experimenter has correctly interpreted the statement of the hypothesis (for example, does the meaning of "sheep" include rams?), finding a black sheep falsifies the "white sheep only" hypothesis. This sort of example probably provides the easiest way to understand the term "hypothesis".

According to Schick and Vaughn (2002), researchers weighing up alternative hypotheses may take into consideration:

• Testibility (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 recognised knowledge-systems

Quotes

• "Hypotheses non fingo" : "I feign no hypotheses" — Isaac Newton¹

• "... a hypothesis is a statement whose truth is temporarily assumed, whose meaning is beyond all doubt. ..." — Albert Einstein²

• "The supreme goal of all theory is to make the irreducible basic elements as simple and as few as possible without having to surrender the adequate representation of a single datum of experience." — Albert Einstein (1933)

See also

• Causality
• Ecological fallacy
• Learning
• Logic
• Null hypothesis
• Philosophiae Naturalis Principia Mathematica for Newton's position on hypotheses
• Reductionism
• Research design
• Scientific method
• Statistical hypothesis testing
• Theory
• Thought experiment
• Null Hypothesis - The Journal of Unlikely Science

Notes

Note 1: Isaac Newton, Principia Mathematica. A New Translation by I. Bernard Cohen and Anne Whitman, translators. University of California Press 1999 ISBN 0-520-08817-4

Note 2: Letter to Eduard Study from Albert Einstein, September 25,1918 Collected Papers of Albert Einstein, J.J. Stachel and Robert Schulmann, eds. Princeton University Press 1987

External links

• Research and Evaluation Glossary

• Analysis and Synthesis - On Scientific Method, based on a study by Bernhard Riemann From the Swedish Morphological Society

References

ISBN links support NWE through referral fees

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

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