Principle of sufficient reason

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The principle of sufficient reason states that anything that happens does so for a definite reason. In virtue of which no fact can be real or no statement true unless it has sufficient reason why it should not be otherwise. It is usually attributed to Gottfried Leibniz,^[1] although the first person to use it was Anaximander of Miletus.^[2]

Contents 1 Formulation 2 Leibniz's view 3 As a Law of Thought 4 Schopenhauer's Four Forms 5 Violations 6 See also 7 Notes 8 External links

[edit] Formulation

The principle has a variety of expressions, all of which are perhaps best summarized by the following:

• For every entity x, if x exists, then there is a sufficient explanation why x exists.
• For every event e, if e occurs, then there is a sufficient explanation why e occurs.
• For every proposition p, if p is true, then there is a sufficient explanation why p is true.

A sufficient explanation may be understood either in terms of reasons or causes for like many philosophers of the period, Leibniz did not carefully distinguish between the two. The resulting principle is very different, however, depending on which interpretation is given.

[edit] Leibniz's view

In fact Leibniz opposed fatalism and had a more nuanced and characteristic version of the principle, in which the contingent was admitted on the basis of infinitary reasons, to which God had access but humans did not. He explained this while discussing the problem of future contingents:

We have said that the concept of an individual substance [Leibniz also uses the term haecceity ] includes once for all everything which can ever happen to it and that in considering this concept one will be able to see everything which can truly be said concerning the individual, just as we are able to see in the nature of a circle all the properties which can be derived from it. But does it not seem that in this way the difference between contingent and necessary truths will be destroyed, that there will be no place for human liberty, and that an absolute fatality will rule as well over all our actions as over all the rest of the events of the world? To this I reply that a distinction must be made between that which is certain and that which is necessary. (§13, Discourse on Metaphysics)

Without this qualification, the principle can be seen as a description of a certain notion of closed system, in which there is no 'outside' to provide unexplained events with causes. It is also in tension with the paradox of Buridan's ass.

[edit] As a Law of Thought

The principle was one of the four recognised laws of thought, that held a place in European pedagogy of logic and reasoning (and, to some extent, philosophy in general) in the eighteenth and nineteenth century. It was influential in the thinking of Leo Tolstoy, amongst others, in the elevated form that history could not be accepted as random.

[edit] Schopenhauer's Four Forms

According to Schopenhauer's On the Fourfold Root of the Principle of Sufficient Reason, there are four distinct forms of the principle.

Principle of Sufficient Reason of Becoming

If a new state of one or several real objects appears, another state must have preceded it upon which the new state follows regularly.

Principle of Sufficient Reason of Knowing

If a judgment is to express a piece of knowledge, it must have a sufficient ground. By virtue of this quality, it receives the predicate true. Truth is therefore the reference of a judgment to something different therefrom.

Principle of Sufficient Reason of Being

The position of every object in space and the succession of every object in time is conditioned by another object's position in space and succession in time.

Principle of Sufficient Reason of Acting

Every human decision is the result of an object that necessarily determines the human's will by functioning as a motive.

[edit] Violations

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• Quantum mechanics, it has been argued, violates the Principle (especially the "event" version) because elementary particles exhibit behavior without any observable external cause, and no internal mechanisms have yet been observed within them. This lack of observable causes for spontaneous quantum events is one of the properties of quantum mechanics that most disturbed Albert Einstein. The Bell test experiments, testing the Einstein-Podolsky-Rosen Paradox, have several times verified that quantum systems behave in a manner inconsistent with either the Principle of Sufficient Reason, or the Axiom of Causality.

Counter Argument

• The above is not an entirely accurate picture of the relationship between the PSR and quantum mechanics. Quantum theory does not allow for an event without a cause/reason. Even virtual particles occur because the potential for their occurrence is contained in the relevant Lagrangian. A true example of a violation of the PSR would be the occurrence of a physical event that did not have a corresponding term in the governing Lagrangian. What quantum mechanics does allow is a cause without necessarily having an effect. For example, throwing a particle at a barrier may or may not cause it to reflect back. However, without some sort of barrier it will never bounce back. Another example is Schroedinger's cat - if the cat is observed to be dead there is a reason (it was poisoned). If it is observed to be alive there is a reason (it was not poisoned). Quantum mechanics forces us to amend our understanding of effect, not cause, and therefore the PSR is not at all violated.

[edit] See also

• Deterministic system (philosophy)
• Law of thought

[edit] Notes

[edit] External links

• The Principle of Sufficient Reason: A Reassessment by Alexander R. Pruss
• A Defense of a Principle of Sufficient Reason by Quentin Smith