It is a popular custom among learned society to toss around the names of theories without explanation or elaboration– Murphy’s Law, Occam’s Razor, and so on. But who were Murphy and Occam, and who are they to come up with these life-governing rules? Below are five well-known rules and laws, and the stories behind their namesakes.

1. Occam’s Razor

Occam’s razor is known more formally as the law of parsimony or the law of economy, and states that “entities should not be multiplied unneccesarily.” Put simply, it is the notion that the simplest explanation is usually the right one. It is named after William of Occam, who was a scholastic philosopher and Franciscan friar that lived in England in the 14th century. His contemporaries were the likes of Thomas Aquinas and the Islamic scholar Averroes. William was the first to write down the principle in its formal wording, and it gained his name due to its frequent usage in medieval philosophy. William was also one of the first to argue that people should not attempt to derive the idea of God from reason or natural logic.

2. Moore’s Law

Moore’s Law is not actually a law, but instead an observation made in 1965 regarding transistors– specifically, that the number of transistors that can be placed inexpensively in an integrated circuit doubles about every two years. The observation was made by Gordon E. Moore, a graduate of UC-Berkeley and Caltech, in an article in the now-defunct Electronics Magazine. Three years after this observation, Moore co-founded Intel Corporation and served in various positions before becoming its chairman and CEO in 1979, and retiring to a chairman emeritus position in 1997. Nowadays, chip manufacturers treat Moore’s Law as a professional challenge, struggling to keep the pace by constantly inventing new ways to squeeze more transistors onto chip surfaces.

3. Murphy’s Law

Murphy’s Law is also less of a law and more of an old saying: “anything that can go wrong, will go wrong.” It is named after Edward Murphy, who was an American aerospace engineer who, funnily enough, worked primarily on safety-critical systems. Most of his efforts went into developing escape systems for experimental aircrafts, such a the F-4 Phantom II and the SR-71 Blackbird. Murphy thought that people in his profession should always consider the worst-case scenario, and so he often cited his old adage as a central tenet of defensive design. However, his efforts to have the law taken seriously were unsuccessful. There also exists a “corollary” to Murphy’s Law, called Finagle’s Law of Dynamic Negatives, which states “anything that can go wrong, will, at the worst possible moment.”

4. Pareto Principle

The Pareto Principle, also known as the “80-20 rule,” is the observation that for many events and sets of data, 80% of the effects come from 20% of the causes. It is named after Vilfredo Pareto, an Italian economist who lived and worked around the turn of the 20th century. In 1906, he noted in his research that 20 percent of the population in Italy owned 80 percent of the the land. He extrapolated this relationship to the general distribution of wealth, noting in a book published in 1909 that this proportion applied roughly across time and location. It wasn’t until much later that the rule was named after Pareto, by business management consultant Joseph Juran. The rule is now applied very widely, not just to wealth but to quality assurance– Microsoft has noted that fixing the most-reported 20% of bugs fixes 80% of errors and crashes– and time management by gurus like Tim Ferriss, author of The 4-Hour Workweek, who encourages people to focus their energies on the 20% of activities that generate 80% of the results. Would-be applicants should use the rule with caution, though– it is meant to illustrate a general majority-minority relationship, and is not a hard-and-fast law applicable to all cases.

5. Parkinson’s Law

Parkinson’s Law states, “work expands so as to fill the time available for its completion.” Despite the fact that it is quoted quite soberly today among efficiency experts, Parkinson’s Law began as a joke. It was the first sentence of a satire piece published in 1955 in The Economist by Cyril Northcote Parkinson. Parkinson was no economist or scientist, but rather a naval historian and professor, first in Liverpool and then in Singapore. After the success of the article, Parkinson expanded upon his piece in a book called Parkinson’s Law. Though the book was only a hundred pages long, it became an instant best seller in the United States.

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