Occam’s Razor

Summary: Occam’s Razor, also known as the Law of Parsimony, is a decision-making philosophy which emphasizes the rationality of simple explanations. If a problem has two possible explanations – a simple one and a complex one – Occam’s Razor rationalizes that the simple explanation is more likely correct.

Originator: William of Ockham (1287-1347)

Keywords: simplicity, Law of Parsimony, Ockham’s Razor, rational, simple explanations, simple hypothesis, scientific inquiry

William of Ockham was a theologian and philosopher who specialized in the area of logic.[i] He spent a lot of time thinking of the best ways to come to logical answers to questions.

Ockham believed that things could only truly be known through self-evidence, experience, or Scripture. In any other situation, Ockham applied his most famous theory, Occam’s Razor. When something isn’t known and there are multiple possible explanations, Ockham believed it was most logical and rational to choose the simpler explanation because it avoided the problem of making assumptions.

Occam’s Razor is most applicable to scientific and mathematical contexts. In many situations, scientists are presented with two or more possible answers to problems or natural phenomenon that they are studying. Occam’s Razor emphasizes creating a working theory around the more simplistic possible answer and concentrating research with that answer in mind.

Occam’s razor is often expressed using the following statement, “Don’t multiply entities beyond necessity.” In other words, keep things as simple as possible, and avoid assumptions and multiple variables as much as possible.

 An Example of Occam’s Razor

An example of Occam’s Razor is often taught to medical students. Professors sometimes tell their students, “When you hear hoof beats, think of horses not zebras.” This statement was coined by Dr. Theodore Woodward, and he used it to teach his students to look for common medical diagnoses over rare ones. When assessing a patient’s symptoms, simpler and more common diagnoses should be considered first. For example, when someone presents with pain in the head, the diagnosis is more likely a headache or a migraine than a brain tumor. When people experience pain in the abdomen, they are more likely experiencing indigestion than cancer. Simple explanations are best.

Occam’s Razor and Scientific Research

Some of the concepts behind Occam’s Razor are still apparent in how scientists go about the process of scientific investigation. This is most applicable in how scientists create hypotheses for a scientific study.[ii] A hypothesis is a scientist’s best guess of what they believe their study will prove. Simple hypotheses are easier to prove than complex hypotheses. A simple hypothesis is one that tests the impact of one variable (the independent) on another variable (the dependent variable). Anytime more variables are added to the picture, the scientific study becomes more complex and the relationships between the variables are harder to prove. By focusing on simplicity – the concept behind Occam’s Razor – scientists can be more accurate and focused in their research.


[i] Spade, P. V. and Panaccio, C. “William of Ockham”, The Stanford Encyclopedia of Philosophy (Winter 2016 Edition), Edward N. Zalta (ed.), URL = <https://plato.stanford.edu/archives/win2016/entries/ockham/>.

[ii] Riesch, H. (2010). “Simple or simplistic? Scientists’ views on Occam’s Razor.” Theoria, 67, 75-90.