Causal principle

Name for a variety of principles, such as that every event has a cause, that the same cause must have the same effect, or that the cause must have at least as much reality as the effect.

This last principle (somewhat akin to the principle of sufficient reason) usually says that what causes something to be of a certain sort must itself be of that sort to at least the same degree; for example, what makes something hot must itself be hot.

This goes back to Aristotle’s principle that actuality is prior to potentiality: that is, what is potentially so-and-so can only be made actually so by something that is itself actually so.


Descartes defends CAP by quoting Roman philosopher Lucretius: “Ex nihilo nihil fit”, meaning “Nothing comes from nothing”.—Lucretius[1]:146–482

In his meditations, Descartes uses the CAP to support his trademark argument for the existence of God.[2]:430 Descartes’ assertions were disputed by Thomas Hobbes in his “Third Set of Objections” published in 1641.[3]:379

René Descartes was not the founder of this philosophical claim.[4]:54–56 It is used in the classical metaphysics of Plato and Aristotle, and features eminently in the works of Thomas Aquinas.


  • A “cause” is that which brings something into effect.
  • If an item has the quality X formally, it has it in the literal or strict sense.
  • If an item has the quality X eminently, it has it in a higher or grander form.

To demonstrate this, a person can possess money formally by holding it on their person, or by storing it in a bank account. Similarly, a person can eminently possess money by owning assets that could readily be exchanged for it.[5]:155–156

Descartes offers two explanations of his own:[6]:28

  • Heat cannot be produced in an object which was not previously hot, except by something of at least the same order of perfection as heat.
  • A stone, for example, which previously did not exist, cannot begin to exist unless it is produced by something which contains, either formally or eminently everything to be found in the stone.

Descartes goes on to claim that the CAP not only applies to stones, but also the realm of ideas, and the features that are seen as part of the objective reality of an idea.[7]:33–35


  1. ^ Carus, T. L., De Rerum Natura (Oxford: Oxford University Press, 1947), pp. 146–482.
  2. ^ Miles, M. L., Inroads: Paths in Ancient and Modern Western Philosophy (Toronto: University of Toronto Press, 2003), p. 430.
  3. ^ Craig, E., ed., The Shorter Routledge Encyclopedia of Philosophy (Abingdon-on-Thames: Routledge, 2005), p. 379.
  4. ^ Campbell, M., Time and Narrative in Descartes’s Meditations, dissertation under the tutelage of profs. P. Magee and A. Dickerson, University of Canberra, January 2018, pp. 54–56.
  5. ^ Feser, E., Scholastic Metaphysics: A Contemporary Introduction (Neunkirchen-Seelscheid: Editiones Scholasticae, 2014), pp. 155–156.
  6. ^ Cottingham, J., Stoothoff, R., & Murdoch, D., trans., The Philosophical Writings of Descartes (Cambridge: Cambridge University Press, 1984), p. 28.
  7. ^ Jolley, N., Causality and Mind: Essays on Early Modern Philosophy (Oxford: Oxford University Press, 2013), pp. 33–35.

Further reading

  • Dicker, G., Descartes: An Analytical and Historical Introduction (Oxford: Oxford University Press, 2013), pp. 118ff.
  • Jolley, N., Causality and Mind: Essays on Early Modern Philosophy (Oxford: Oxford University Press, 2013).

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