Occam's Razor

Ockham’s Razor, in its most general definition, is a philosophical principle that states that when choosing between competing hypotheses, the one with fewer assumptions should be preferred. It is often summarized by the phrase “Entities should not be multiplied beyond necessity” (Entia non sunt multiplicanda praeter necessitatem). This principle does not claim that simplicity is a guarantee of truth; rather, it argues that when theories have equal explanatory power, it is rational to choose the one with fewer unproven assumptions.

Ockham’s Razor is a principle known by several other names:

• Principle of Simplicity
• Principle of Parsimony
• Economy of Thought

The core logic of the principle is to avoid introducing unnecessary complexity or unverified entities when explaining a phenomenon. The metaphor of the “razor” derives from the idea of “cutting away” or “shaving off” superfluous assumptions in a theory. For example, two hypotheses might be proposed to explain the phenomenon of crop circles: 1) they were created by alien spacecraft, or 2) they were made by pranksters. Ockham’s Razor recommends favoring the second hypothesis because it does not require assuming the existence of UFOs—whose existence lacks any clear evidence—but only accepts a well-documented human behavior that has been frequently observed throughout history.

The principle proposes a principle of economy: avoid multiplying unnecessary entities in a set of propositions, eliminate redundancies, and prioritize the most straightforward option.

The roots of the principle of simplicity extend far earlier than the English philosopher William of Ockham, all the way back to Aristotle. Before Ockham, thinkers such as Ibn al-Haytham (965–1040), Maimonides (1138–1204), and Duns Scotus (1266–1308) also defended similar ideas.

The most prominent representative of the principle is the late medieval philosopher and theologian William of Ockham (1285–1347). For this reason, the principle bears his name. William of Ockham was born in the village of Ockham, in Surrey, near London. He studied at the University of Oxford and is regarded as one of the most influential thinkers of the 14th century.

Interestingly, it is noted that William of Ockham never used the exact phrase “Entities should not be multiplied beyond necessity” in any of his works. However, this understanding is widely accepted as consistent with the spirit of his philosophy. According to philosopher Bertrand Russell, although Ockham did not use this specific wording, he did express ideas such as “it is vain to do with more what can be done with less.” The term “Ockham’s Razor” was first used by the British mathematician Sir William Rowan Hamilton in 1852.

One of the first to apply the principle of simplicity in its modern sense was Copernicus (1473–1543), a founder of the scientific revolution. However, it was the Austrian physicist and philosopher Ernst Mach (1838–1916) who placed the principle at the center of scientific methodology. Mach referred to it as “economy of thought” and regarded it as a law that science ought to follow.

The application and interpretation of Ockham’s Razor vary. There are multiple interpretations and limitations of the principle.

The principle can be formulated logically as follows:

• Premise 1: Two theories, T1 and T2, explain the observed phenomena equally well, but T1 requires accepting the existence of more entities than T2.
• Premise 2 (Ockham’s Razor): If two theories explain the phenomena equally well, one should believe the theory that makes fewer assumptions without sacrificing explanatory power.
• Conclusion: One should believe T2.

Ockham’s Razor can be understood differently depending on how it is applied:

• Quantitative vs. Qualitative Razor: The quantitative razor aims to reduce the number of individual entities (e.g., explaining an event with nine people instead of eleven). The qualitative razor seeks to reduce the number of types of entities (e.g., if concrete objects can explain everything, then accepting abstract objects is unnecessary).
• Strong vs. Weak Razor: The strong razor rejects the existence of entities that add no explanatory power. The weak razor takes an agnostic stance regarding such entities, refraining from asserting either their existence or non-existence. William of Ockham himself applied the principle not in the strong (denying) sense but in the weak (skeptical) sense. According to him, one should not believe in the existence of anything whose existence cannot be known through one of three sources: self-evident truth, empirical evidence, or divine revelation.

Ockham’s Razor is frequently misunderstood:

1. Simplicity does not imply truth: The razor does not claim that “the simple is true” or “the complex is false.” It only states that when explanatory power is equal, the hypothesis with fewer assumptions should be preferred.
2. Explanatory power takes precedence: If a theory has greater explanatory power, it should be preferred even if it requires more entities or assumptions. For example, Einstein’s Theory of Relativity is more complex than Newton’s Theory of Gravity, but because it explains more phenomena, Ockham’s Razor does not require preferring Newton’s theory.
3. It does not define what is simple: The principle itself does not determine which explanation involves fewer or more assumptions. This assessment is independent of the principle’s application.
4. It does not encourage inaction: The absence of a reason to choose between two options does not require inaction. As in the case of Buridan’s Ass, remaining paralyzed between two bales of hay until starving to death is not rational; one must choose one.

The logic of Ockham’s Razor has influenced a broad range of fields, from philosophy to science, theology to art.

Accepted by many scientists and analytic philosophers, the principle serves as a guide in selecting among scientific theories: when two models explain the data equally well, the one requiring less theoretical baggage is preferred.

• Kalam Cosmological Argument: Philosophers such as William Lane Craig invoke Ockham’s Razor when arguing that the universe must have a first cause, and debating whether this cause is singular or multiple. Craig argues that “we should disregard the possibility of multiple uncaused causes and favor the assumption of a single first cause,” using the razor to defend the existence of one first cause (God). Critics argue that this application is flawed, because there is insufficient basis to prefer a single or multiple cause, and the razor merely imposes an arbitrary choice in this context.
• Naturalism: Naturalist thought uses the principle of simplicity to regard supernatural explanations as unnecessary. For example, when explaining a child’s birth, natural causes such as sexual reproduction are sufficient; invoking the will of a transcendent God is seen as an unnecessary complication. This view “shaves off” explanations involving external first causes or divine intervention, relying solely on natural laws.
• Protestantism: Martin Luther’s reforms can be interpreted as a form of “simplification” analogous to Ockham’s Razor. Luther eliminated intermediary institutions such as the Papacy, church councils, and saints between the individual and God, reducing the relationship to “faith alone” (sola fide) and “grace alone” (sola gratia). This can be viewed as an effort to simplify theological structure by removing what were deemed “unnecessary” entities.
• Salafism: A similar logic appears in some interpretations of Salafi thought. This approach “shaves off” centuries of accumulated theoretical methods, contextual interpretations, and sectarian traditions, advocating direct engagement with religious texts. For instance, rejecting practices such as visiting tombs or seeking intercession, which are seen as unnecessary intermediaries between God and the believer, exemplifies this simplifying logic.

• Minimalism: The foundation of the minimalist movement can be seen as rooted in the philosophy of Ockham’s Razor. The idea of eliminating unnecessary elements to focus on the essence is central to minimalist art.
• Graphic Design: A practical example is American graphic designer Lanny Sommese’s “Apple” lesson. Sommese drew an apple on the board and wrote “Apple” beneath it, then asked students which was redundant. This illustrates the principle of conveying a message in the simplest and most direct way possible.
• Mark Rothko: The later period of artist Mark Rothko’s career has been analyzed as an artistic application of Ockham’s Razor. Rothko removed figurative and surrealist elements from his work, using only large fields of color (“color fields”) to directly convey emotions such as pain, pleasure, and sorrow. This represents an effort to eliminate “unnecessary” narrative layers between the viewer and the artwork.

The KISS principle (“Keep it Simple, Stupid”) used in engineering and other technical fields is a modern analogue of Ockham’s Razor. This principle argues that avoiding unnecessary complexity leads to systems that are more reliable and efficient.