[4.18.4] Ockham’s Razor

In the treatise of an unknown author, “On the Principles of Theology,” and other medieval works, we can find some statements attributed to William Ockham (1285-1349 AD), all of them formulating the principle of Ockham’s razor:

  • “Beings are not to be multiplied beyond necessity.”
  • “Plurality is not to be posited without necessity.”
  • “What can happen through fewer [principles] happens in vain through more.”
  • “When a proposition is verified of things, more [things] are superfluous if fewer suffice.”

Ockham himself uses two strategies for the elimination of redundant entities: he analyzes if there is a good reason for the existence of the entity; and if the existence of the entity leads to falsehood, as presented on the UML Activity Diagram below:

Ockham’s razor
Analyze & understand the reasons and consequences of the ENTITYAnalyze & understand the reasons and consequences of the Entity
Is there a good reason for the ENTITY?“Ockham has two main lines of attack against other people’s ontologies. One proceeds by arguing that the reasons others give for postulating certain entities are not good reasons, that everything that can be done with such entities can be done without them. This is the main strategy he uses, for example, to argue that real entities
are not needed in most of Aristotle’s ten categories. Combined with
Ockham’s Razor, this approach implies not only that such entities
are unnecessary, but that therefore they should not be postulated.”
Is the existence of the ENTITY leading to a falsehood?“Ockham has two main lines of attack against other people’s ontologies. […] The second main line of attack is different. It argues that certain other people’s ontological theories not only postulate unnecessary entities but lead to plain falsehood – either to self-contradiction or, at least, to claims that contradict established facts. This is one of the ways Ockham argues, for example, against realist theories of universals.”
Eliminate ENTITYEliminate ENTITY from the theory – apply Ockam’s razor
Confirm ENTITYConfirm ENTITY


  • All citations from: Spade, Paul Vincent, “Ockham’s Nominalist Metaphysics”, The Cambridge Companion to Ockham, ed. Paul Vincent Spade, Cambridge University Press, 2006
  • Spade, Paul Vincent and Claude Panaccio, “William of Ockham”The Stanford Encyclopedia of Philosophy (Spring 2019 Edition), Edward N. Zalta (ed.)

First published: 20/11/2021

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