William of Ockham (Occam)

Occam’s Razor explained: When you hear hoofbeats think horses, not zebras

Occam’s razor, a foundational principle in philosophy and science, postulates that when presented with multiple explanations for a phenomenon, the simplest one – requiring the fewest assumptions – is often the most likely to be correct. Named after the 14th-century Franciscan friar, William of Ockham, this heuristic tool champions simplicity and clarity over complexity. At its core, Occam’s razor underscores the value of parsimony in reasoning, suggesting that unnecessary complications in a hypothesis can deter us from the truth. While not an infallible rule, it serves as a guiding light, reminding us that straightforward explanations, free from unwarranted intricacies, often lead the way to genuine understanding.


The principle of Occam’s razor finds its roots in the works of the medieval philosopher and theologian, William of Ockham. Hailing from the English village of Ockham in the 14th century, he frequently employed a Latin phrase that translates to: “Entities should not be multiplied without necessity.” While William never directly formulated Occam’s razor, his writings consistently leaned towards simpler explanations for theological and philosophical matters.

The essence of the principle, favoring simplicity, predates Ockham. Ancient thinkers like Aristotle hinted at similar ideas, emphasizing simplicity in explanations. Over time, Occam’s razor gained prominence, influencing various fields from science to philosophy. Renowned scientists, including Galileo and Newton, implicitly used this heuristic, preferring simpler hypotheses that adequately explained observations. Today, Occam’s razor remains a fundamental guideline, championing clarity and cautioning against overcomplication.

Although the term “Occam’s razor” became popular several centuries after William of Ockham’s passing in 1347, its origins can be traced back to him. The first reference to this principle in association with Ockham was made by the theologian and scientist Libert Froidmont (1587-1653) in his work, “On Christian Philosophy of the Soul”, where he mentions “novacula occami”.

While Ockham didn’t originate this principle, its widespread recognition and its linkage to him might be attributed to the consistent and effective manner he applied it in his writings. Ockham expressed the principle in various forms. However, the most cited rendition, “Entities are not to be multiplied without necessity” (Non sunt multiplicanda entia sine necessitate), came from the Irish Franciscan philosopher John Punch in 1639, when he commented on Duns Scotus’s works.

Occam’s Razor explained

Occam’s razor is the idea that the simplest explanation is usually the right one. Imagine you hear hoofbeats outside your window. Instead of thinking it’s a rare zebra, it’s more likely a common horse. This idiom, “When you hear hoofbeats think horses, not zebras”, captures the essence of Occam’s razor. For instance, if your TV stops working, it’s more likely that it’s unplugged than the idea that aliens disabled it. Or if your plant is wilting, it probably needs water rather than assuming it’s reacting to a rare disease. The principle suggests we should first consider the simplest solutions, as they require fewer assumptions.

Occam’s razor can be understood using the fundamentals of probability theory. Every event or phenomenon has a likelihood, or probability, of occurring. When we formulate theories or explanations, each assumption we introduce carries its own probability. The more assumptions we add, the more chances there are for potential inaccuracies. Think of it like adding more variables to an equation: each new variable can increase the chance of an error. If an assumption doesn’t enhance a theory’s precision, it merely amplifies the chances the theory might be off-mark.

That said, it’s essential to understand that Occam’s razor is not an unbreakable rule but rather a guiding principle in reasoning. Its core message isn’t to always opt for the most straightforward theory blindly. If a complex explanation better accounts for the observed facts and data, then its intricacy is warranted. In science, as with many disciplines, the ultimate judge should be empirical evidence; observations and experiments should dictate which theories hold water, regardless of their simplicity or complexity.

William of Ockham (Occam)
William of Ockham depicted on a stained glass window at All Saints’ Church, Ockham. He championed the idea that when faced with multiple explanations for a phenomenon, the simplest one – requiring the fewest assumptions – is often the most likely to be correct. This principle, “Occam’s Razor”, has since become a cornerstone in scientific inquiry and critical thinking.

Occam’s Razor and other logical tools

Occam’s razor, Hitchens’s razor, and the Sagan standard are guiding principles that steer critical thinking, especially when evaluating claims and hypotheses. Here are their similarities:

  • Evidence-based Reasoning: All three principles underscore the importance of grounding conclusions in evidence. While they approach the topic from different angles, the foundational idea is the same: claims should be based on solid evidence, and beliefs without evidence can and should be questioned.
  • Simplifying Complexities: Both Occam’s razor and the Sagan standard lean towards simplification. Occam’s razor suggests choosing the explanation with the fewest assumptions, while the Sagan standard (often paraphrased as “extraordinary claims require extraordinary evidence”) implies that more complex or extraordinary claims need stronger evidence.
  • Burden of Proof: Hitchens’s razor and the Sagan standard focus on the burden of proof. Hitchens’s razor suggests that if a claim is made without evidence, it can be dismissed just as easily, and the Sagan standard implies that the depth of evidence required corresponds to the magnitude of the claim.
  • Guard against Gullibility: Each principle, in its own way, serves as a safeguard against gullibility and promotes skeptical inquiry. They encourage individuals to challenge assertions, particularly those that lack empirical support or seem implausible.
  • Enhancing Scientific Rigor: These principles are often invoked in scientific discussions to ensure rigor. By emphasizing evidence and simplicity, they guide scientists and thinkers to formulate hypotheses and conclusions that are both robust and parsimonious.

While each principle has its unique nuances, they collectively promote critical thinking, skepticism, and the pursuit of knowledge rooted in evidence and logic.

Occam’s Razor and the Complexities of Biology

Francis Crick, who alongside James Watson unveiled the double helix structure of DNA, highlighted that Occam’s razor’s call for “simplicity and elegance” may not always apply neatly to the intricate domain of biology. He gives the theory of Darwinian evolution by natural selection as an example. This concept is, according to Crick, more intricate than attributing all life forms to a divine creator’s handiwork. Yet, despite its complexity, evolution aligns more cohesively with the empirical facts and observations we’ve amassed over time.

But I don’t agree with him. In fact, evolution, despite its seeming complexity, is a much simpler answer, so it is compatible with Occam’s Razor. Here’s why:

“God created everything” might appear simple at face value, but when applied as an explanatory tool, it raises more questions than it answers. Here’s a breakdown:

  • Lack of Mechanism: Saying “God created everything” provides no detailed mechanism or process. How was life created? Over what time span? Why were certain creatures made? Without answers to these, the statement becomes a placeholder rather than an explanation.
  • Infinite Regress: If one posits that God created everything, the immediate question is, “Who or what created God?” This leads to a potential infinite regress without a satisfactory conclusion.
  • Variability Across Cultures: Different cultures have various gods and creation stories. Which one is accurate? Relying on “God created everything” necessitates navigating and reconciling a myriad of religious texts and beliefs.

Evolution is a much more simple answer:

  • Based on Evidence: The theory of evolution is grounded in a wealth of empirical evidence, from the fossil record to genetic data. It offers a coherent narrative of life’s development, based on observations and verifiable experiments.
  • Mechanistic & Predictive: Evolution provides mechanisms (e.g., natural selection, genetic drift) that explain how species change over time. It can make predictions about what we might expect to find in the fossil record or how species might adapt to environmental changes.
  • Consistent with Other Scientific Theories: Evolution dovetails with findings in other scientific fields, such as paleontology, genetics, and biochemistry. It’s not just a standalone explanation but part of an interconnected web of scientific understanding.

In summary, while “God created everything” might seem like a straightforward explanation, it’s laden with unresolved complexities. Evolution, on the other hand, provides a more straightforward, evidence-based account of life’s diversity and development, making it, in many ways, a simpler and more comprehensive answer.


M. Özgür Nevres


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