As I often mention, I love a proverb, fable, aphorism, koan, and teaching stories of all kinds.

I also love any rule described by someone as a “razor” or a “law” or a “paradox.” Over the years, I’ve collected these, and I find them enormously helpful in my understanding of the world.

As you’ll see, some are actually scientific or based on patterns uncovered in research; others are based on individual observation; others are jokes.

Here are some of my favorites:

Jevons Paradox: Increased efficiency in resource use can lead to increased consumption of that resource; in the long term, efficiency gains generate an increase in consumption rather than a decrease. The economist William Stanley Jevons was noting that as Britain became more efficient at using coal, the country consumed more coal, not less.

Moravec’s Paradox: With AI and robotics, what’s hard is easy and what’s easy is hard — it’s easier to train computers on mathematics and logic, harder to train them on walking and image recognition.

Hanlon’s Razor: Never attribute to malice that which is adequately explained by stupidity.

Kranzberg’s Law: I love this one! “Technology is neither good nor bad; nor is it neutral.”

Hitchens’s Razor: “What can be asserted without evidence can also be dismissed without evidence.” Christopher Hitchens, who was well-known for making the case for atheism, made this point in arguments about religious claims.

Related…

Sagan Standard: Extraordinary claims require extraordinary evidence.

Pareto Principle: For many phenomena, 80% of consequences stem from 20% of the causes. For instance, a friend who is a literary agent said, “A small number of my clients take up most of my time, and they aren’t even my most successful clients.”

Arthur C. Clarke’s Third Law: Any sufficiently advanced technology is indistinguishable from magic.  I think we are starting to experience this!

Amara’s Law: We tend to overestimate the effect of a technology in the short run and underestimate the effect in the long run.

Alder’s Razor: What can’t be settled by experiment is not worth debating. This reminds me of one of my darker Secrets of Adulthood: “People find arguments particularly satisfying when nothing can be proven and nothing can be refuted.”

Popper’s principle of falsifiability: For a theory to be considered scientific, it must be falsifiable. For instance, “all swans are white” could be proven false, but “everything happens for a reason” can explain just about anything. Note—an idea could be valuable even if it isn’t scientific.

Hofstadter’s Law: It always takes longer than you expect, even when you take into account Hofstadter’s Law. Hofstadter framed his law in terms of time, but I’ve found it also applies to money. When we were doing some renovations on our apartment, we were advised to add an extra 20% to our budget, as a cushion for hidden problems–but then it actually cost 20% on top of that.

Parkinson’s Law: Work expands to fill the time available for its completion. Corollary: Expenditure rises to meet income.

Acton’s dictum: Power tends to corrupt, and absolute power corrupts absolutely.

Bechdel test: A film passes if (1) it has at least two women, (2) who talk to each other, (3) about something other than a man.

Occam’s Razor: Among competing explanations, prefer the simplest one that adequately accounts for the evidence. For instance, an hour has gone by and your child hasn’t answered your text. The simplest explanation is that she’s busy and forgot to answer your text. Another explanation is that she got into a car crash and is now unconscious in a hospital.

Law attributed to Ward Cunningham: The best way to get the right answer on the internet is not to ask a question; it’s to post the wrong answer.

Reilly’s law of retail gravitation: When two cities (or shopping centers) compete for the trade of a town between them, each draws customers in proportion to its population and in inverse proportion to the square of the distance shoppers must travel. In other words, we go to the bigger mall, but not if we have to drive too far.

Cromwell’s rule: Never assign a probability of exactly 0 or 1 to anything that isn’t a logical certainty, so that evidence can always change your mind. The Bayesian statistician Dennis Lindley named this rule after the statesman Oliver Cromwell, who, in 1650, appealed to the Church of Scotland to change their position on a crucial matter of state: “I beseech you, in the bowels of Christ, think it possible you may be mistaken.”

Chekhov’s gun: Every element in a story must be necessary, and irrelevant elements should be removed. If a rifle is hanging on the wall in act one, it must fire by the end, or it shouldn’t be hanging there.

Weber’s law–the just-noticeable difference between two stimuli is proportional to their magnitude. That is, we notice proportional changes more than absolute changes. We notice an extra ounce of weight added to a mixing bowl much more easily than the same ounce added to a bowling ball.

I love these laws, razors, and rules so much that I can’t resist adding my own:

Gretchen Rubin’s Law: To understand how people behave, consider whether they meet or resist inner expectations (such as a New Year’s resolution) and outer expectations (such as a work deadline). This, of course, is the key to my “Four Tendencies” framework that divides people into Upholders, Questioners, Obligers, and Rebels. Take the free, quick quiz.

Speaking of my Four Tendencies framework, perhaps it’s because I’m an Upholder that I love a list of rules like these. They help me understand the world much better.