Ibn Sina's Treatises on Possible and Necessary Existence

Ibn Sina, On Possible and Necessary Existence

In the treatises that Ibn Sina (980-1037) devotes to metaphysics in The Book of Healing (Kitab al-Shifa), he draws a distinction between possible and necessary existence. He argues that necessary existence belongs only to that which exists through itself and to that which does not depend on anything other than itself for its own existence. Possible existence belongs to anything that does not exist through itself, and to that which depends on something other than itself for its own existence.

If something is caused to exist, then its existence is not through itself. Something that exists through itself does not depend for existence upon anything other than itself.

Anything that can possibly exist depends upon being caused to exist or not exist; if nothing causes it to exist, then it does not exist. If it were to exist without being caused to exist, it would already have to exist through itself.

For something to necessarily exist through itself, it must have a sufficient nature for necessary existence. If something does not necessarily exist through itself, then its possible existence depends upon whether or not it is caused to exist.

The existence of that which does not have a sufficient nature for necessary existence depends upon an existing cause; the absence of an existing cause for existence causes its nonexistence.1

Anything that can possibly exist can only exist if it becomes necessary in relation to its cause. If it is not necessary in relation to a given cause for its existence, then it must be necessary in relation to another cause for its existence.

Ibn Sina argues that a sufficient nature for necessary existence is not shared by more than one existing being. If it could be shared by more than one existing being, then one being that necessarily exists through itself could be co-equal with another being that necessarily exists through itself. Each of the two beings would necessarily exist, and would also possibly exist through the other co-equal being. But this would be contradictory to their relation as co-equal beings, Ibn Sina says, because each could exist through itself without depending for existence on the other.

If something necessarily exists through itself, then there cannot be anything else that necessarily exists through itself. If there were more than one existing being that could necessarily exist through itself, then it would be possible for an existing being to be simultaneously necessary through itself and not necessary through itself. This is a contradiction, says Ibn Sina. Necessary existence cannot be limited to possible existence. Thus, there can only be one existing being which is necessary through itself.

Ibn Sina says that every aspect of that which necessarily exists is necessary. Necessary existence cannot be relative or changing. Necessary existence is an absolute unity, and not a plurality.

According to Ibn Sina, something that exists through itself cannot be divided into parts. If it could be divided into parts, then it would have a principle of differentiation that would determine how it could be divided into parts. But the essence of an existing being is not differentiated, and thus the principle of differentiation cannot proceed directly from the essence itself. Thus, the principle of differentiation must come from causes external to the essence of that being. But this would mean that non-essential consequences would have to occur in that being, even though it necessarily exists through itself. This would be contradictory to its necessary existence, says Ibn Sina. Thus, if something exists through itself, it is not differentiated into a plurality of parts.

Ibn Sina argues that necessary being is free from a cause to bring its essence into existence, because it has no essence other than existence. But he also asserts that necessary being has other attributes, such as pure good, pure reason, and pure truth.2

Ibn Sina’s proof for the existence of God consisted in the argument that possible beings ultimately depend for their existence upon a being necessary through itself. This proof was later accepted by Maimonides and Aquinas, but rejected by Ibn Rushd.3

In Aristotelian terms, possible being has potentiality, and necessary being has actuality. Possible being can be actualized only by that which is already actualized. Possible being ultimately depends upon an existing being which is fully actualized.

Ibn Sina’s view of possible and necessary existence reflects his own interpretation of Islamic faith. For Ibn Sina, necessary existence can only belong to one Necessary Being. This reflects the teaching of the Qur’an that there is only one God.4

Ibn Sina was later criticized by al-Ghazali, however, for saying that the world is created as an eternal emanation of being from Necessary Being, which al-Ghazali held was not in accordance with the teachings of the Qur’an.5

Ibn Sina’s interpretation of necessary and possible existence explains the difference between probabilty and certainty. Necessary existence is existential certainty. Necessary existence is not an attribute of probability, but of certainty. According to Ibn Sina, we must depend for our existence upon that which is necessary through itself. This reflects the view that we are limited by existential uncertainty, which can be transcended by faith in God.


1Avicenna, First Treatise from “The Healing, Metaphysics,” translated by Arthur Hyman, in Philosophy in the Middle Ages, ed. by Arthur Hyman and James J. Walsh (Indianapolis: Hackett Publishing Company, 1973), p. 242.

2Majid Fakhry, A Short Introduction to Islamic Philosophy, Theology and Mysticism (Oxford: Oneworld Publications, 1997), p. 51.

3 Arthur Hyman and James J. Walsh, “Avicenna” in Philosophy in the Middle Ages (Indianapolis: Hackett Publishing Company, 1973), p. 235.

4 A.M. Goichon, The Philosophy of Avicennna and Its Influence on Medieval Europe, translated by M.S. Khan (Delhi: Motilal Banarsidass, 1969), p. 15.

5Arthur Hyman and James J. Walsh, “Avicenna” in Philosophy in the Middle Ages (Indianapolis: Hackett Publishing Company, 1997), pp. 234-6.

BIBLIOGRAPHY

Avicenna, Excerpts from al-Risalat al-'Arshiya, translated by Arthur J. Arberry, in Avicenna on Theology by Arthur J. Arberry, Westport: Hyperion Press, (1951), pp. 25-37.

Fakhry, Majid. A Short Introduction to Islamic Philosophy, Theology and Mysticism. Oxford: Oneworld Publications, (1997), pp. 47-54.

Hyman, Arthur, and Walsh, James J. Philosophy in the Middle Ages. Indianapolis: Hackett Publishing Company, (1973), pp. 234-255.

Goichon, A.M. Translated by M.S. Khan. The Philosophy of Avicenna and Its Influence on Medieval Europe. Delhi: Motilal Banarsidass, (1969), pp. 1-46.

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