Jul 23, 2014

Understanding Hypothesis, Theory and Law


The terms hypothesis, theory and law have precise meanings when used in science. Generally speaking, these terms all try to provide reasonable descriptive statements about specific phenomena. The big difference, however, is the levels of confidence attributed to these terms.

The levels of scientific confidence are based on the reliability of predicted result as verified by independent experiments. Hypotheses typically have the lowest scientific confidence while theories and laws have the highest levels of scientific confidence because they are well-tested and peer-reviewed by scientists.

Contrary to common understanding, hypothesis, theory and law do not necessarily imply a continuum. A hypothesis does not always graduate into theory or law. Similarly, a law is not necessarily more well-established than a theory.


A scientific hypothesis is a tentative explanation about a particular phenomenon, set of observable facts or implications that remains to be tested. It could be derived either through deductive or inductive reasoning based on previous observations and established scientific theories or laws. Multiple hypotheses can also be proposed, refined and combined to provide a more coherent and comprehensive explanation. This typically becomes a working hypothesis, which is a provisionally accepted hypothesis that is subject to further research.

According to Schick and Vaughn, scientists who are evaluating and comparing various hypotheses should take into consideration the following criteria:

Testability or falsifiability
Parsimony or the application of “Occam's razor”
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

Scientific hypotheses typically have high mortality when they are subjected to a barrage of tests. Very few hypotheses survive to be accepted as factual. Most hypotheses do not lead to breakthroughs even if they become a well-established fact. A hypothesis could be as mundane and narrow as explaining why there is a mold growth in a supposedly sterilized agar medium in a Petri dish or it could be a grand and complex as explaining how it is possible for biological life to arise from simple organic molecules.


Contrary to common notion, a scientific theory is not a merely speculative explanation. A scientific theory is rigorously tested to the point that it becomes a very reliable and comprehensive explanation about some aspects of nature. A theory is well-supported by a vast body of evidence that typically comes from multidisciplinary approach. The tests for the validity of a scientific theory are independently done by various experts in a particular field of inquiry, complying with the strictest scientific protocols and other criteria of modern science. A theory is proposed in a way that it can either be empirically verified or contradicted (falsified).

Scientific theories have the characteristics of being capable of providing accurate predictions. In contrast to hypotheses, which are empirically testable conjectures, theories have already undergone and survived several empirical tests done by independent scientists.

Theories may either be modified in the light of additional evidence or they may be integrated with other theories to form a synthesis such as such as in the case of the modern synthesis of genetics with the Darwinian Theory of evolution through natural selection. Very few theories well-established theories are completely overthrown.

Historically speaking, few paradigms shifts or scientific revolutions had completely overthrown well-established theories. Some common examples include the following: geocentric theory overthrown by heliocentric theory, absolute space-time theory overthrown by relativity theory, and steady state theory overthrown by the big bang theory.


A scientific law is similar to a scientific theory in terms of empirical support and wide acceptability among the experts in a particular field. However, the main differences of a scientific law with a theory include comprehensiveness, predictive capability and explanatory ability. Laws and theories are interrelated and do not have degrees of superiority compared to each other. It is a misconception to assume that a law is more established than a theory.

A law is a descriptive statement about a specific phenomenon while a theory is the explanation behind that phenomenon. In most cases scientific laws are contained within theories. For example, the three Mendelian laws of inheritance are contained within the theory of genetics. The Medelian laws describe the phenomenon of inheritance while the genetic theory explains the cause and mechanism of inheritance.

For example, the first law of inheritance (Law of Segregation) states that every individual contains a pair of alleles for each particular trait which segregate or separate before cross breeding for any particular trait and that each parent passes a randomly selected copy (allele) to its offspring. This is well-established fact that is observable when breeding diploid organisms. However, this law does not explain why it happens or how it happens.

Scientific laws are narrower in scope while theories are much broader and comprehensive. For example, the Newtonian law on universal gravitation does not apply in very strong gravitational fields such as in the case of black holes. This law may describe planetary motions and projectile trajectories but does not provide an explanation. By comparison, Einstein’s special theory of relativity does not only account for the planetary motions and projectile trajectories but explains gravity as the curvature of space-time, thereby providing explanation as to how and why the paths of motions are curved. More precise calculations can also be made using Einstein’s theory.

Philosophical Views

Scientific hypotheses, theories and laws are all based on empiricism or the idea that a valid test for truth must be based on sensory experience and evidence. As a branch of epistemology, science is primarily concerned with verifiable and provable knowledge. Hence, scientific knowledge is a posteriori knowledge.

On a stricter sense, scientific hypotheses, theories and laws are limited to methodological naturalism. This means that science is limited by facts and ideas that can be experimentally tested or empirically observed. It is based on the assumption that nature is coherent, consistent and self-explanatory.

On one hand, the logical positivists assume that scientific concepts in the forms of hypotheses, theories and laws can be deduced based on the axioms of nature. On the other hand, the semantic view assumes that scientific concepts are both inductive and deductive in nature but only provides models or approximation of reality rather than revealing the fundamental and consequential state of nature.


1. http://austringer.net/wp/index.php/2009/07/03/another-look-at-law-and-theory/
2. http://www.livescience.com/21457-what-is-a-law-in-science-definition-of-scientific-law.html
3. http://www.differencebetween.net/miscellaneous/culture-miscellaneous/difference-between-theory-and-law/
4. http://en.wikipedia.org/wiki/Scientific_law
5. http://www.merriam-webster.com/dictionary/theory
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.

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