# List of eponymous laws

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This list of eponymous laws provides links to articles on laws, theorems, principles, adages, and other succinct observations or predictions named after a person. In some cases the person named has coined the law – such as Parkinson's law. In others, the work or publications of the individual have led to the law being so named – as is the case with Moore's law. There are also laws ascribed to individuals by others, such as Murphy's law; or given eponymous names despite the absence of the named person.

## C–D

• Campbell's law – "The more any quantitative social indicator is used for social decision making, the more subject it will be to corruption pressures and the more apt it will be to distort and corrupt the social processes it is intended to monitor."[1] Named after Donald T. Campbell (1916–1996)
• Cassie's law – Describes the effective contact angle θc for a liquid on a composite surface.
• Cassini's laws – provide a compact description of the motion of the Moon. Established in 1693 by Giovanni Domenico Cassini.
• Celine's laws – Celine's laws are a series of three laws regarding government and social interaction attributed to the fictional character Hagbard Celine from Robert Anton Wilson's The Illuminatus! Trilogy.
• Charles's law – States that at constant pressure, the volume of a given mass of a gas increases or decreases by the same factor as its temperature (in kelvins) increases or decreases. Named after Jacques Charles.
• Child's law – States that the space-charge limited current in a plane-parallel diode varies directly as the three-halves power of the anode voltage and inversely as the square of the distance separating the cathode and the anode. Named after Clement D. Child; also known as the Child-Langmuir Law (after Irving Langmuir). See also Mott–Gurney law.
• Chladni's law – Relates the frequency of modes of vibration for flat circular surfaces with fixed center as a function of the numbers of diametric (linear) nodes and of radial (circular) nodes. Named after Ernst Chladni.
• Claasen's law – Theo Claasen's "logarithmic law of usefulness" – 'usefulness = log(technology)'.
• Clarke's three laws – Formulated by Arthur C. Clarke. Several corollaries to these laws have also been proposed.
• First law: When a distinguished but elderly scientist states that something is possible, he is almost certainly right. When he states that something is impossible, he is very probably wrong.
• Second law: The only way of discovering the limits of the possible is to venture a little way past them into the impossible.
• Third law: Any sufficiently advanced technology is indistinguishable from magic.
• Conway's law – Any piece of software reflects the organizational structure that produced it. Named after Melvin Conway.
• Cooper's law – The number of radio frequency conversations which can be concurrently conducted in a given area doubles every 30 months.
• Cope's rule – Population lineages tend to increase in body size over evolutionary time.
• Coulomb's law – An inverse-square law indicating the magnitude and direction of electrostatic force that one stationary, electrically charged object of small dimensions (ideally, a point source) exerts on another. It is named after Charles-Augustin de Coulomb.
• Cunningham's law – The best way to get the right answer on the Internet is not to ask a question, it’s to post the wrong answer. Attributed to Ward Cunningham by Steven McGeady.
• Curie's law – In a paramagnetic material the magnetization of the material is (approximately) directly proportional to an applied magnetic field. Named after Pierre Curie.
• D'Alembert's principle – States that the sum of the differences between the forces acting on a system of mass particles and the time derivatives of the momenta of the system itself along any virtual displacement consistent with the constraints of the system, is zero. Named after Jean le Rond d'Alembert.
• Dale's principle – In neuroscience, states that a neuron is capable of producing and secreting only one neurotransmitter from its axon terminals. Named after Henry Hallett Dale but more recent data suggests it to be false. A more common interpretation of the original statement made by Dale is that neurons release the same set of transmitters at all of their synapses.
• Dalton's law – In chemistry and physics, states that the total pressure exerted by a gaseous mixture is equal to the sum of the partial pressures of each individual component in a gas mixture. Also called Dalton's law of partial pressure, and related to the ideal gas laws, this empirical law was observed by John Dalton in 1801.
• Darcy's law – In hydrogeology, describes the flow of a fluid (such as water) through a porous medium (such as an aquifer).
• Davis' law – In anatomy, describes how soft tissue models along imposed demands. Corollary to Wolff's law.
• De Morgan's laws – Apply to formal logic regarding the negation of pairs of logical operators.
• Dennard scaling - States that the computing performance per watt grows exponentially at roughly the same rate as Moore's law.
• Dermott's law – The sidereal period of major satellites tends to follow a geometric series. Named after Stanley Dermott.
• Dilbert principle – Coined by Scott Adams as a variation of the Peter Principle of employee advancement. Named after Adams' Dilbert comic strip, it proposes that "the most ineffective workers are systematically moved to the place where they can do the least damage: management."
• Doctorow's law - "Anytime someone puts a lock on something you own, against your wishes, and doesn't give you the key, they're not doing it for your benefit."
• Dolbear's law – an empirical relationship between temperature and the rate of cricket chirping.
• Dollo's law – "An organism is unable to return, even partially, to a previous stage already realized in the ranks of its ancestors." Simply put this law states that evolution is not reversible.
• Dulong–Petit law – States the classical expression for the specific heat capacity of a crystal due to its lattice vibrations. Named for Pierre Louis Dulong and Alexis Thérèse Petit.
• Dunbar's number – A theoretical cognitive limit to the number of people with whom one can maintain stable social relationships. No precise value has been proposed for Dunbar's number, but a commonly cited approximation is 150. First proposed by British anthropologist Robin Dunbar.
• Dunning–Kruger effect – Is a cognitive bias in which unskilled individuals suffer from illusory superiority, mistakenly rating their ability much higher than average. This bias is attributed to a metacognitive inability of the unskilled to recognize their mistakes.
• Duverger's law – After Maurice Duverger. Winner-take-all (or first-past-the-post) electoral systems tend to create a 2 party system, while proportional representation tends to create a multiple party system.

## H–K

• Haber's rule – A mathematical statement relating the concentration of a poisonous gas and how long it must be breathed to result in death.
• Haitz's law – an observation and forecast about the steady improvement, over many years, of light-emitting diodes (LEDs).
• Hamilton's principle – States that the dynamics of a physical system is determined by a variational problem for a functional based on a single function, the Lagrangian, which contains all physical information concerning the system and the forces acting on it. Named after William Rowan Hamilton.
• Hanlon's razor – A corollary of Finagle's law, and a play on Occam's razor, normally taking the form, "Never attribute to malice that which can be adequately explained by stupidity." As with Finagle, possibly not strictly eponymous. Alternatively, "Do not invoke conspiracy as explanation when ignorance and incompetence will suffice, as conspiracy implies intelligence."
• Hartley's law – A way to quantify information and its line rate in an analog communications channel. Named for Ralph Hartley (1888–1970).
• Hauser's law – Empirical observation about U.S. tax receipts as a percentage of GDP, theorized to be a natural equilibrium.
• Hawthorne effect – A form of reactivity whereby subjects improve an aspect of their behavior being experimentally measured simply in response to the fact that they are being studied. Named after Hawthorne Works.
• Hebb's law – "Neurons that fire together wire together."
• Heisenberg's Uncertainty principle – States that one cannot measure values (with arbitrary precision) of certain conjugate quantities, which are pairs of observables of a single elementary particle. The most familiar of these pairs is position and momentum.
• Henry's law – The mass of a gas that dissolves in a definite volume of liquid is directly proportional to the pressure of the gas provided the gas does not react with the solvent.
• Herblock's law – "If it's good, they'll stop making it." Possibly coined by Herbert Lawrence Block, whose pen name was Herblock.
• Hess's law – In physical chemistry, the total enthalpy change during the complete course of a reaction is the same whether the reaction is made in one step or in several steps.
• Hick's law – In psychology, the time it takes for a person to make a decision as a function of the number of possible choices.
• Hitchens's razor – An epistemological principle maintaining that the burden of evidence in a debate rests on the claim-maker, and that the opponent can dismiss the claim if this burden is not met.
• Hofstadter's law – "It always takes longer than you expect, even when you take into account Hofstadter's Law" (Douglas Hofstadter, Gödel, Escher, Bach, 1979).
• Hooke's law – The tension on a spring or other elastic object is proportional to the displacement from the equilibrium. Frequently cited in Latin as "Ut tensio sic vis." Named after Robert Hooke (1635–1703).
• Hotelling's law in economics – Under some conditions, it is rational for competitors to make their products as nearly identical as possible.
• Hubble's law – Galaxies recede from an observer at a rate proportional to their distance to that observer. Formulated by Edwin Hubble in 1929.
• Hume's law – In meta-ethics, the assertion that normative statements cannot be deduced exclusively from descriptive statements.
• Humphrey's law – conscious attention to a task normally performed automatically can impair its performance. Described by psychologist George Humphrey in 1923.
• Hund's rules - Three rules in atomic physics used to determine the term symbol that corresponds to the ground state of a multi-electron atom. Named after Friedrich Hund.
• Hutber's law – "Improvement means deterioration." Coined by financial journalist Patrick Hutber.
• Isaac Bonewits's laws of magic – "Laws" synthesized from a multitude of belief systems from around the world, collected in order to explain and categorize magical beliefs within a cohesive framework.
• Jevons paradox – The proposition that technological progress that increases the efficiency with which a resource is used tends to increase (rather than decrease) the rate of consumption of that resource.
• Joule's laws – Heat laws related to electricity and to gasses, named for James Prescott Joule.
• Kepler's laws of planetary motion – Describe the motion of the planets around the sun. First articulated by Johannes Kepler.
• Kerckhoffs' principle of secure cryptography – A cryptosystem should be secure even if everything about the system, except the key, is public.
• Kirchhoff's laws – One law in thermodynamics and two about electrical circuits, named after Gustav Kirchhoff.
• Klaiber's law – That the silicon wafer size will dictate the largest diameter of ultrapure water supply piping needed within a semiconductor wafer factory.
• Koomey's law – That the energy of computation is halved every year and a half.
• Kopp's law – The molecular heat capacity of a solid compound is the sum of the atomic heat capacities of the elements composing it. Named for Hermann Franz Moritz Kopp.
• Korte's law – The greater the length of a path between two successively presented stimuli, the greater the stimulus onset asynchrony must be for an observer to perceive the two stimuli as a single moving object.
• Kranzberg's laws of technology – The first law states that technology is neither good nor bad; nor is it neutral.

## L–M

• L'Hôpital's rule – This rule uses derivatives to find limits of indeterminate forms 0/0 or ±∞/∞, and only applies to such cases.
• Lanchester's laws – formulae for calculating the relative strengths of predator/prey pair and application in military conflict.
• Landauer's principle – Asserts that there is a minimum possible amount of energy required to change one bit of information, known as the Landauer limit.
• Leibniz's law – A principle in metaphysics also known as the Identity of Indiscernibles. It states: "If two objects have all their properties in common, then they are one and the same object."
• Lenz's law – An induced current is always in such a direction as to oppose the motion or change causing it.
• Lewis's law – The comments on any article about feminism justify feminism.
• Liebig's law of the minimum – The growth or distribution of a plant is dependent on the one environmental factor most critically in demand.
• Linus' law – "Given enough eyeballs, all bugs are shallow." Named for Linus Torvalds.
• Little's law – In queuing theory, "The average number of customers in a stable system (over some time interval) is equal to their average arrival rate, multiplied by their average time in the system." The law was named for John Little from results of experiments in 1961.
• Littlewood's law – States that individuals can expect miracles to happen to them, at the rate of about one per month. Coined by Professor J E Littlewood, (1885–1977).
• Lotka's law – In infometrics, states that the number of authors publishing a certain number of articles is a fixed ratio to the number of authors publishing a single article. As the number of articles published increases, authors producing that many publications become less frequent. For example, there may be 1/4 as many authors publishing two articles within a specified time period as there are single-publication authors, 1/9 as many publishing three articles, 1/16 as many publishing four articles, etc. Though the law itself covers many disciplines, the actual ratios involved are very discipline-specific.
• Malthusian growth model – Also referred to as the Malthusian law or simple exponential growth model, is exponential growth based on a constant rate. The model is named after Thomas Robert Malthus, who wrote An Essay on the Principle of Population (1798), one of the earliest and most influential books on population.
• Marconi's law – An empirical law that relates radio communication distance to antenna tower height
• Meadow's law – A precept, now discredited, that since cot deaths are so rare, "One is a tragedy, two is suspicious and three is murder, until proved otherwise." It was named for Sir Roy Meadow, a discredited paediatrician prominent in the United Kingdom in the last quarter of the twentieth century.
• Mendel's laws – Named for the 19th century Austrian monk Gregor Mendel who determined the patterns of inheritance through his plant breeding experiments, working especially with peas. Mendel's first law, or the law of segregation, states that each organism has a pair of genes; that that it inherits one from each parent, and that the organism will pass down only one of these genes to its own offspring. These different copies of the same gene are called alleles. Mendel's second law, the law of independent assortment, states that different traits will be inherited independently by the offspring.
• Menzerath's law, or Menzerath–Altmann law (named after Paul Menzerath and Gabriel Altmann), is a linguistic law according to which the increase of a linguistic construct results in a decrease of its constituents, and vice versa.
• Metcalfe's law – In communications and network theory, states that the value of a system grows as approximately the square of the number of users of the system. Framed by Robert Metcalfe in the context of ethernet.
• Miller's law – In communication, states: "To understand what another person is saying, you must assume that it is true and try to imagine what it could be true of." Named after George Armitage Miller. In psychology, states that the number of objects an average person can hold in working memory is about seven. Also named after George Miller. In software development, states: "All discussions of incremental updates to Bugzilla will eventually trend towards proposals for large scale redesigns or feature additions or replacements for Bugzilla." Named after Dave Miller.
• Miller's Rule – In optics, an empirical rule which gives an estimate of the order of magnitude of the nonlinear coefﬁcient.
• Mooers' law – "An information retrieval system will tend not to be used whenever it is more painful and troublesome for a customer to have information than for him not to have it." An empirical observation made by American computer scientist Calvin Mooers in 1959.
• Moore's law – An empirical observation stating that the complexity of integrated circuits doubles every 24 months. Outlined in 1965 by Gordon Moore, co-founder of Intel.
• Moravec's paradox – "it is comparatively easy to make computers exhibit adult level performance on intelligence tests or playing checkers, and difficult or impossible to give them the skills of a one-year-old when it comes to perception and mobility."
• Muphry's law – "If you write anything criticizing editing or proofreading, there will be a fault of some kind in what you have written." The editorial equivalent of Murphy's law, according to John Bangsund.
• Murphy's law – "Anything that can go wrong will go wrong." Ascribed to Edward A. Murphy, Jr.

## N–Q

• Naismith's rule – A rule of thumb that helps in the planning of a walking or hiking expedition by calculating how long it will take to walk the route, including ascents.
• Neuhaus's law – Where orthodoxy is optional, orthodoxy will sooner or later be proscribed. This "law" had been expressed earlier. For example, Charles Porterfield Krauth wrote in his The Conservative Reformation: "Truth started with tolerating; it comes to be merely tolerated, and that only for a time. Error claims a preference for its judgments on all disputed points."
• Newton's law of cooling – The rate of cooling (or heating) of a body due to convection is proportional to the difference between the body temperature and the ambient temperature.
• Newton's laws of motion – In physics, three scientific laws concerning the behaviour of moving bodies, which are fundamental to classical mechanics (and since Einstein, which are valid only within inertial reference frames). Discovered and stated by Isaac Newton (1643–1727), they can be formulated, in modern terms, as follows:
• First law: "A body remains at rest, or keeps moving in a straight line (at a constant velocity), unless acted upon by a net outside force."
• Second law: "The acceleration of an object of constant mass is proportional to the net force acting upon it."
• Third law: "Whenever one body exerts a force upon a second body, the second body exerts an equal and opposite force upon the first body."
• Niven's laws: "If the universe of discourse permits the possibility of time travel and of changing the past, then no time machine will be invented in that universe."
• Nyquist rate – The minimum sampling rate required to avoid aliasing is equal to twice the highest frequency contained within the signal. Named after Harry Nyquist.
• Occam's razor – States that explanations should never multiply causes without necessity. ("Entia non sunt multiplicanda praeter necessitatem.") When two or more explanations are offered for a phenomenon, the simplest full explanation is preferable. Named after William of Ockham (ca.1285–1349).
• Ohm's law – In physics, states that the ratio of the potential difference (or voltage drop) between the ends of a conductor (and resistor) to the current flowing through it is a constant. Discovered by and named after Georg Simon Ohm (1789–1854).
• Ohm's acoustic law – An empirical approximation concerning the perception of musical tones, named for Georg Simon Ohm.
• Okrent's law - Daniel Okrent's take on the argument to moderation.
• Okun's law – In economics, this refers to the trend that every time unemployment increases by 1%, a 2% decrease in the annual GDP occurs.
• Orgel's rules – In evolutionary biology, a set of axioms attributed to the evolutionary biologist Leslie Orgel.
• First rule: "Whenever a spontaneous process is too slow or too inefficient a protein will evolve to speed it up or make it more efficient."
• Second rule: "Evolution is cleverer than you are."
• Papert's principle – "Some of the most crucial steps in mental growth are based not simply on acquiring new skills, but on acquiring new administrative ways to use what one already knows."
• Pareto optimality – Given an initial allocation of goods among a set of individuals, a change to a different allocation that makes at least one individual better off without making any other individual worse off is called a Pareto improvement. An allocation is defined as "Pareto efficient" or "Pareto optimal" when no further Pareto improvements can be made.
• Pareto principle – States that for many phenomena 80% of consequences stem from 20% of the causes. Named after Italian economist Vilfredo Pareto, but framed by management thinker Joseph M. Juran.
• Parkinson's law – "Work expands to fill the time available for its completion." Corollary: "Expenditure rises to meet income." Coined by C. Northcote Parkinson (1909–1993).
• Parkinson's law of triviality – "The time spent on any agenda item will be in inverse proportion to the sum of money involved." Also due to C. Northcote Parkinson.
• Peter principle – "In a hierarchy, every employee tends to rise to his level of incompetence." Coined by Dr. Laurence J. Peter (1919–1990) in his book The Peter Principle. In his follow-up book, The Peter Prescription, he offered possible solutions to the problems his principle could cause.
• Planck's law – In physics, describes the spectral radiance of a black body at a given temperature. After Max Planck.
• Plateau's laws – Describe the structure of soap films. Named after Belgian physicist Joseph Plateau.
• Poe's law (poetry) – There is a maximum desirable length for poems: "The unit of poetry must be fixed by the reader's capacity of attention, and ... the limits of a poem must accord with the limits of a single movement of intellectual apprehension and emotional exaltation," named for Edgar Allan Poe.[2][3] See "The Philosophy of Composition".
• Poe's law (religious fundamentalism) – "Without a winking smiley or other blatant display of humour, it is impossible to create a parody of fundamentalism that someone won't mistake for the real thing."[4] named after Nathan Poe who formulated it on the Web site Christian Forums in 2005.[5] Although it originally referred to creationism, the scope later widened to religious fundamentalism.[6]
• Poisson's law of large numbers – For independent random variables with a common distribution, the average value for a sample tends to the mean as sample size increases. Named after Siméon Denis Poisson (1781–1840) and derived from "Recherches sur la probabilité des jugements en matière criminelle et en matière civile" (1837; "Research on the Probability of Criminal and Civil Verdicts").
• Postel's law – Be conservative in what you do; be liberal in what you accept from others. Derived from RFC 761 (Transmission Control Protocol, 1980) in which Jon Postel summarized earlier communications of desired interoperability criteria for the Internet Protocol (cf. IEN 111)[7]
• Powell doctrine – In foreign policy, that specific questions are answered before initiating a military conflict (e.g. clear achievable objective, overwhelming force to minimize casualties, exit strategy).
• Premack's principle – More probable behaviors will reinforce less probable behaviors. Named by David Premack (1925 – )
• Pythagorean theorem – is a relation in Euclidean geometry among the three sides of a right triangle (right-angled triangle). The Pythagorean theorem is named after the Greek mathematician Pythagoras

## T–Z

• Thomas theorem – "If men define situations as real, they are real in their consequences," a social law as far as there are any. (After W.I. Thomas and D.S. Thomas.)
• Titius–Bode law – "a hypothesis that the bodies in some orbital systems, including the Sun's, orbit at semi-major axes in a function of planetary sequence". Named for Johann Daniel Titius and Johann Elert Bode.
• Tobler's first law of geography – "Everything is related to everything else, but near things are more related than distant things." Coined by Waldo R. Tobler (b. 1930).
• Tully–Fisher relation – Stated by R. Brent Tully and J. Richard Fisher, relates the intrinsic luminosity of a galaxy to its velocity width.
• Vegard's law – In metallurgy, an approximate empirical rule which holds that a linear relation exists, at constant temperature, between the crystal lattice parameter of an alloy and the concentrations of the constituent elements. Named for Lars Vegard.
• Verdoorn's law – In economics, this law pertains to the relationship between the growth of output and the growth of productivity. According to the law, faster growth in output increases productivity due to increasing returns. Named after Dutch economist, Petrus Johannes Verdoorn.
• Verner's law – Stated by Karl Verner in 1875, Verner's law describes a historical sound change in the Proto-Germanic language whereby voiceless fricatives *f, *þ, *s and *x, when immediately following an unstressed syllable in the same word, underwent voicing and became respectively *b, *d, *z and *g.
• Wagner's law – Predicts that the development of an industrial economy will be accompanied by an increased share of public expenditure in gross national product, and is named after the German economist Adolph Wagner (1835–1917).
• Walras' law - States that budget constraints imply that the values of excess market demands must sum to zero.
• Weber–Fechner law – This law named after the Germans Ernst Heinrich Weber and Gustav Theodor Fechner attempts to describe the human perception of various physical stimuli. In most cases, Stevens' power law gives a more accurate description.
• Werther effect - A spike of emulation suicides after a widely publicized suicide, named after the protagonist of Goethe's novel The Sorrows of Young Werther.
• Weyl law – In Mathematics, describes the asymptotic behavior of eigenvalues of the Laplace-Beltrami operator. Named for Hermann Weyl.
• Wike's law of low odd primes – "If the number of experimental treatments is a low odd prime number, then the experimental design is unbalanced and partially confounded." (Wike, 1973, pp. 192–193).[10]
• Wirth's law – Software gets slower faster than hardware gets faster.
• Wolff's law – Bone adapts to pressure, or a lack of it.[11]
• Woodward–Hoffmann rules – in organic chemistry predicting the stereochemistry of pericyclic reactions based on orbital symmetry.
• Yao's principle – In computational complexity theory, states that the expected cost of any randomized algorithm for solving a given problem, on the worst case input for that algorithm, can be no better than the expected cost, for a worst-case random probability distribution on the inputs, of the deterministic algorithm that performs best against that distribution. Named for Andrew Yao.
• Zawinski's law – Every program attempts to expand until it can read mail. Those programs which cannot expand are replaced by ones which can.
• Zeigarnik effect – Named after Bluma Zeigarnik; people remember uncompleted or interrupted tasks better than completed tasks.
• Zipf's law – In linguistics, the observation that the frequency of use of the nth-most-frequently-used word in any natural language is approximately inversely proportional to n, or, more simply, that a few words are used very often, but many or most are used rarely. Named after George Kingsley Zipf (1902–1950), whose statistical body of research led to the observation. More generally, the term Zipf's law refers to the probability distributions involved, which are applied by statisticians not only to linguistics but also to fields remote from that.

## References

1. ^ Campbell, Donald T., Assessing the Impact of Planned Social Change The Public Affairs Center, Dartmouth College, Hanover New Hampshire, USA. December, 1976.
2. ^ Murry, John M. (1923/1969). Pencillings. Ayer Publishing. p. 88. ISBN 0-8369-1229-2. Check date values in: `|date=` (help)
3. ^ as cited in Monte, Steven (2000). Invisible fences: prose poetry as a genre in French and American literature. Lincoln: University of Nebraska Press. pp. 145. ISBN 0-8032-3211-X.
4. ^ Chivers, Tom (2009-10-23). "Internet rules and laws: the top 10, from Godwin to Poe". The Daily Telegraph (London). Retrieved 2009-10-25.
5. ^ Poe, Nathan (August 11, 2005). "Big contradictions in the evolution theory". Christian Forums. p. 6. Retrieved 2009-10-25.
6. ^ Aikin, Scott (2009-01-22). "Poe's Law, Group Polarization, and the Epistemology of Online Religious Discourse". SSRN. Retrieved 2010-05-19.
7. ^
8. ^ "The General Glut Controversy". The New School for Social Research (NSSR). Archived from the original on March 19, 2009.
9. ^ Evans, Leonard; Schwing, Richard C (1985). Human behavior and traffic safety. Plenum Press. ISBN 978-0-306-42225-6.
10. ^ Wike, E. L. (1973). Water beds and sexual satisfaction: Wike’s law of low odd primes (WLLOP). Psychological Reports, 33, 192-194.
11. ^ Anahad O'Connor (October 18, 2010). "The Claim: After Being Broken, Bones Can Become Even Stronger". New York Times. Retrieved 2010-10-19. This concept – that bone adapts to pressure, or a lack of it – is known as Wolff’s law.