Occam's razor - Stained Glass window with likeness of William of Ockham at All Saints' Church, Ockham

What is Occam’s razor? – a Simple Explanation

Occam’s razor is a medieval problem-solving principle stating, “With all things being equal, the simplest explanation tends to be the right one.”

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What is Occam’s razor?

In plain English, Occam’s razor states, “With all things being equal, the simplest explanation tends to be the right one.” Or put another way: Of any given set of explanations for an event occurring, the simplest one is most likely the correct one.

It is a medieval problem-solving principle attributed to William of Ockham (1287-1347), a Franciscan friar and philosopher. His theories follow the principle of simplicity.

Occam’s razor
“With all things being equal, the simplest explanation tends to be the right one.”
William of Ockham (1287-1347)

In its original Latin, Occam’s razor is:

“Pluralitas non est ponenda sine necessitate“,

which translates as

“Plurality should not be posited without necessity.”

What is an example of Occam’s razor

Some examples of Occam’s razor are:

Bright Light on Road? UFO or Street Lamp

When travelling on a deserted country road at night and suddenly blinded by a bright light. Is it:

  1. a bright street lamp or
  2. a UFO?

Answer: The bright street lamp is the simplest of the two explanations and requires the least assumptions.

Noise in Ceiling? Ghost or Possum

You hear a noise in the ceiling. Is it:

  1. a ghost is haunting the house or
  2. a possum on the roof.

Answer: The likelihood of a possum on the roof is the simplest explanation and requires the least number of assumptions.

Homework not handed in? Stolen or Not Done

In the TV show Psych, during a flashback scene, Shawn’s father gets a call from his young son’s teacher saying that Shawn did not hand in his homework.

  1. Shawn claimed someone stole his homework or
  2. Shawn did not do his homework?

Answer: The likelihood that Shawn did not do his homework is the simplest explanation and requires the least number of assumptions.

Occam's razor - Stained Glass window with likeness of William of Ockham at All Saints' Church, Ockham
Photo: Moscarlop, Creative Commons via Wikimedia Commons

Why is Occam’s razor called a ‘razor’?

The phrase was first coined in 1852 by Sir William Hamilton, an Irish mathematician. His writings credit the principle to William of Ockham and name it after him. The term razor refers to shaving away any unnecessary assumptions in different theories.

Occam’s razor - All Saints' Church, Ockham will old graveyard in front.
Photo: [email protected]gChurchPics

Who was William of Ockham

William of Ockham was born around 1287 in the small town of Ockham, twenty-five miles southwest of London, England. There is minimal biographical information on him. He joined the Franciscan order in 1306 in Ockham and studied theology at Oxford University.

The Franciscans’ vow of poverty heavily influenced William of Ockham. He took this view of living and applied it to many areas of his life and writings. His ability to reduce the theory of simplicity to a single sentence helps explain why it has survived.

His writings and theories focused on reason and logic and challenged the religious orthodoxy of the time. In 1323, the Papal Court summoned him to Avignon to answer charges of heresy. In 1328, after four years of arrest, he escaped with other Franciscans to the court of Louis of Bavaria, which was sympathetic to their plight. William of Ockham lived the rest of his life in Germany and continued to write.

This map shows the location of Ockham, in Surrey, South of London in the United Kingdom.

The Theory of Simplicity

The ideas that form the basis for Occam’s razor existed before William’s time. The teachings of Aristotle and French philosopher Peter John Olivi influenced William of Ockham.

The Greek philosopher, Aristotle (384–322 BC), wrote about simplicity being perfection. Famous Greek mathematician Ptolemy (AD 90 -168) lived in Alexandria, Egypt, during the Roman Empire and proposed the use of the simplest hypothesis possible.

Einstein and Stephen Hawking apply Occam’s razor in their theories and writings.

These concepts have an obvious present-day application in system and web design. Keeping the solution and user interface as simple as possible is essential to good design. Simplicity is fundamental for good mobile app design.

Occam's Razor - Movie Poster of Contact (1999) showing Jodie Foster and Matthew McConaughey in front of the Very Large Array (VLA) Antennas.
Photo: Warner Bros

The scientific and mathematics community was familiar with Occam’s razor for centuries. However, a broader audience has become exposed to it by its use in Popular Culture. For example, the Jodie Foster movie Contact (1999), based on the book by Carl Sagan, prominently references Occam’s razor.

This movie was where I first heard about it. The film uses Occam’s razor to challenge the Jodie Foster character’s (Ellie Arroway) account of what happened when she claimed to have travelled through a wormhole in the alien-designed ship. In the movie, Ellie, a scientist, gets put on the back foot when a member of the Congressional Committee uses it to discredit her account of her travels.

Popular TV show references include The X-Files, Fringe, House and Castle episodes.

YouTube video: Contact (1997) – Jodie Foster’s Testimony – I had an experience speech.

Who doesn’t agree with Occam’s razor

Not everyone agrees with the theorem, in particular, many scientists. They claim it obstructs scientific progress when additional research would help understand new theories and information.

Occam’s razor makes no absolute assertions. It does not claim that the simplest explanation is always correct. It merely suggests that, of all possible explanations, the most likely is the one that requires the fewest assumptions.

One of the central elements of problem-solving and decision-making is not solely making the correct choice. Instead, eliminate as many unsuitable alternatives until you reach only a few remaining left. This process is where concepts like Occam’s razor are invaluable. You would eliminate all choices that require too many assumptions.

This wisdom from the Middle Ages is still relevant today.

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