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Comparison: Avicenna & Aristotle
Aristotle (384–322 BCE) founded classical logic and metaphysics. Ibn Sina (980–1037 CE), honoured as “al-Shaykh al-Ra’is”, inherited Aristotle’s system but transformed it from a philosophy grounded in motion into one grounded in existence.
1. Necessary and Contingent Existence
Aristotle
Aristotle analyses being through the categories (substance and accidents) and the pair potentiality–actuality. His guiding question is “what is being qua being?”, and he answers it through substance. He discusses necessity and possibility in logic and physics, but the world does not need to be “given existence”: the cosmos and its substances are eternal, and the question of why anything exists at all has no independent place in his system.
Ibn Sina
Ibn Sina divides whatever can be conceived, with respect to existence, into three: the necessary, the possible (contingent) and the impossible. The Necessary Existent in itself cannot be supposed not to exist; its existence is from itself. The contingent in itself is indifferent to being and non-being and becomes “necessary through another” only through an external cause. Thus the whole world, though eternal, receives its existence at every moment from the Necessary Existent. (al-Shifa, Metaphysics I; al-Najat)
Key innovation: Ibn Sina moves dependence from motion to existence itself.
2. Aristotle's Unmoved Mover and Ibn Sina's Proof of the Truthful
Aristotle
In Physics VIII and Metaphysics Λ, Aristotle begins from the fact of motion: whatever moves is moved by something, and the series of movers cannot go on infinitely, so there must be an unmoved mover. It is pure actuality without matter and moves the cosmos not by pushing but “as an object of love”. His theology is therefore cosmological, arising from the physics of the heavenly spheres.
Ibn Sina
In the fourth namat of al-Isharat wa-l-Tanbihat, Ibn Sina offers a proof that needs neither motion nor creatures, only reflection on existence itself: something exists; it is either necessary or contingent. If necessary, the conclusion follows. If contingent, it needs a cause, and the totality of contingents, even if infinite, is itself contingent and needs a cause outside it, which must be necessary. He calls this the method of “the truthful” (al-siddiqin), because it witnesses the Necessary through existence itself rather than through its effects.
Aristotle reaches a mover; Ibn Sina reaches a giver of being: his God causes existence, not merely motion.
3. The Distinction of Essence and Existence
Aristotle
Aristotle distinguishes logically between “what it is” (given in a definition) and “that it is” (Posterior Analytics II.7) and holds that being is not a genus. In his ontology, however, an actual substance simply is the existent; existence is not treated as something added to essence.
Ibn Sina
Ibn Sina turns this into a metaphysical principle: one can fully conceive a triangle without knowing whether it exists; so existence lies outside essence and “occurs to” it. Essence in itself is neither existent nor non-existent. In every contingent being essence and existence are two, but in the Necessary Existent there is no essence other than existence (“the First has no quiddity other than its being”).
This distinction later became central in Islamic philosophy (Suhrawardi, Mulla Sadra) and for Thomas Aquinas.
4. Causality
Aristotle
Aristotle lists four causes: material, formal, efficient and final (Physics II.3; Metaphysics V.2). The efficient cause is mainly the “source of change”, and the highest explanation is teleological: the Unmoved Mover is the final cause of the cosmos.
Ibn Sina
Ibn Sina accepts the four causes but splits the efficient cause in two: the natural agent, which only produces motion, and the divine agent, which “bestows existence”. The effect depends on its cause for its continued existence, not merely for its coming to be. A true cause and effect are simultaneous, and once the complete cause is present the effect necessarily exists.
For Ibn Sina, causation is above all a relation of giving existence.
5. Eternity or Creation
Aristotle
Aristotle's world has no beginning or end: motion and time are eternal, since any first motion would require a prior motion (Physics VIII.1). The Unmoved Mover did not create the world.
Ibn Sina
Ibn Sina also holds the world to be temporally eternal, but calls it “essentially originated”: it emanates (fayd) eternally from the Necessary Existent and is posterior to it in essence, not in time. Creation is a necessary, everlasting procession, not an act in time. Al-Ghazali sharply criticised this view in The Incoherence of the Philosophers.
Difference: Aristotle's world is eternal and self-standing in being; Ibn Sina's is eternal yet always dependent.
6. The Intellects
Aristotle
In Metaphysics XII.8 Aristotle posits an unmoved mover for each celestial sphere (47 or 55). God is “thought thinking itself”. In De Anima III.5 he briefly mentions an “active” intellect, a terse passage that later generated many commentaries.
Ibn Sina
Ibn Sina builds a system of emanation on the principle “from the One only one proceeds”: from the Necessary Existent proceeds only the First Intellect; by contemplating its source, itself and its own contingency, it gives rise to the next intellect, a celestial soul and a celestial body. The chain continues to the tenth, the Active Intellect, the “Giver of Forms”, which bestows forms on the sublunary world and intelligibles on the human soul.
Ibn Sina's Active Intellect bridges cosmology and the theory of knowledge.
Summary Table
| Topic | Aristotle | Ibn Sina |
|---|---|---|
| Starting point | Motion | Existence |
| God | Unmoved Mover, final cause | Necessary Existent, efficient cause of being |
| Essence/existence | Logical distinction | Metaphysical distinction |
| The world | Eternal, self-standing | Eternal, dependent (emanation) |
| Intellects | Movers of spheres | Emanation chain to the Active Intellect |
Sources
- Aristotle, Physics II, VIII; Metaphysics V, XII (Λ); De Anima III.5; Posterior Analytics II.7
- Ibn Sina, al-Shifa: al-Ilahiyyat (The Metaphysics of The Healing), trans. M. E. Marmura (Brigham Young University Press, 2005)
- Ibn Sina, al-Najat; al-Isharat wa-l-Tanbihat, namat 4
- al-Ghazali, Tahafut al-Falasifa (The Incoherence of the Philosophers)
- Dimitri Gutas, Avicenna and the Aristotelian Tradition (Brill, 2nd ed. 2014)
- Jon McGinnis, Avicenna (Oxford University Press, 2010)
- Stanford Encyclopedia of Philosophy: “Ibn Sina’s Metaphysics”; “Aristotle’s Metaphysics”