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Published online by Cambridge University Press:  26 August 2010

Department of Philosophy, Lehigh University, 15 University DriveBethlehem, Pennsylvania 18015, USA Email:


The medieval Islamic philosophers held a certain conception of the divine unity that assumes the necessary existent to be both one and simple. The oneness of the necessary existent meant that it is the only necessary existent and its simplicity meant that it admits no composition whatsoever – it is pure essence and its essence is necessary existence. In The Incoherence of the Philosophers al-Ġazālī presents, with elaboration, an exposition of the philosophers' conception of the divine unity, several arguments for its two components (i.e., oneness and simplicity), and his critique of these arguments. In this paper I focus on six of the arguments attributed to the philosophers. Following the textual evidence, I reconstruct these arguments and offer two possible interpretations of them. The first interpretation, which I call the many-argument interpretation, sees one of the arguments as employing the simplicity of the necessary existent to establish its oneness and the other five arguments as invoking oneness to establish simplicity. The second interpretation, which I call the one-argument interpretation, doesn't offer a new reading for the first argument but sees the other five arguments as defending the simplicity of the necessary existent based on its basic concept. I argue for the superiority of the one-argument interpretation.


Les philosophes de l'Islam classique ont une doctrine de l'unité divine selon laquelle l'existant nécessaire est à la fois unique et simple. Son unicité signifie qu'il est le seul existant nécessaire, sa simplicité qu'il n'admet aucune sorte de composition; il est pure essence et son essence est existence nécessaire. Dans la Destruction des Philosophes, al-Ġazālī présente avec force détails un exposé de la doctrine de l'unité divine des philosophes, plusieurs arguments en faveur de ses deux composantes (l'unicité et la simplicité), ainsi que sa critique de ces arguments. Je me concentre ici sur six des arguments qu'il attribue aux philosophes. En suivant les données textuelles, je reconstruis ces arguments et en propose deux interprétations possibles. La première, que j'appelle l'interprétation “à arguments multiples”, identifie l'un des arguments comme s'appuyant sur la simplicité de l'existant nécessaire pour établir son unicité, et les cinq autres comme s'appuyant sur son unicité pour établir sa simplicité. La seconde, que j'appelle l'interprétation “à argument unique”, conserve la première lecture du premier argument mais voit dans les cinq autres une défense de la simplicité de l'existant nécessaire fondée sur sa notion fondamentale. J'argumente en faveur de la supériorité de l'interprétation “à argument unique”.

Research Article
Copyright © Cambridge University Press 2010

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1 Muḥammad al-Ġazālī, Abū Ḥāmid, Tahāfut al-Falāsifa, ed. Dunyā, Sulaymān, 7th edn (Cairo, 1987)Google Scholar .

2 Following many translators, I use ‘necessary existent’ to translate the Arabic ‘wāğib al-wuğūd’. Hence, a necessary existent is an existent whose existence is necessary by virtue of itself. According to this usage, God is a necessary existent, but the First Intellect, for example, is not a necessary existent because its existence is necessary by virtue of another – namely, its creator. Another way of defining wāğib al-wuğūd is as an existent that has no cause.

3 A cause is temporal if it brings about its effect after nonexistence. In this case the effect temporally follows its cause. If the effect is synchronous with the cause, the cause is essential. It is prior to the effect in essence, not in time. The philosophers believed that God is the essential first cause of the world, while al-Ġazālī maintained the more traditional view that God created the world after nonexistence. One might want to say that according to al-Ġazālī God is temporally prior to the world. However, the matter is more complex than this, because al-Ġazālī also maintains that time is created with the world; so before there was the world, there was no time. In what sense then did God precede the world? One way of describing the situation is to say that there was God and there was no world, then there was God and there was the world and God brought the word into existence. Whether this is successful in removing the attribution of temporality to God could be debated.

4 al-Ḥusayn Ibn Sīnā, Abū ʿAlī, al-Nağat, ed. ʿUmayara, ʿAbdulrahmān, 2 vols. (Beirut, 1992), vol. I, pp. 79108Google Scholar .

5 al-Ḥusayn Ibn Sīnā, Abū ʿAlī, al-Šifāʾ: al-Ilāhiyyāt, ed. Anawati, Father G. C. and Zāyid, Saʿīd (Qum, 2007), pp. 4347 and 343370Google Scholar .

6 al-Ḥusayn Ibn Sīnā, Abū ʿAlī, al-Išārāt wa-al-Tanbīhāt, ed. al-Zāriʿī, Muğtabā (Qum, 2002), pp. 270275Google Scholar .

7 Al-Ġazālī, Tahāfut al-Falāsifa, pp. 160–95.

8 Ibid., pp. 161–2. (All translations from the Arabic in this paper are mine.)

9 Ibid., pp. 196–7. Although al-Ġazālī rejects the philosophers' version of the cosmological argument, he does believe that an argument of this sort is correct. He doesn't discuss, with detail, his argument in the Tahāfut, but he gives an exposition of it in al-Iqtiṣād fī al-Iʿtiqād (Moderation in Belief), ed. Ibrahim Agâh Çubukçu and Hüseyin Atay (Ankara, 1962), pp. 24–35. (I am currently working on a translation of this book.)

10 The argument need not be restricted to the case of two necessary existents. It can be straightforwardly applied to the general case of two or more necessary existents.

11 He challenges P3 because he wants to challenge C1. The declared goal of the Fifth Discussion of the Tahāfut is to show the philosophers' inability to prove the oneness of God. Of course, al-Ġazālī accepts the doctrine of the oneness of God independently; he only thinks that the philosophers' arguments for the oneness of God are unsound.

12 In other words, indiscernibles are identical. In Western philosophy, this is usually referred to as “Leibniz's Law.”

13 It should be clear that the First Principle is God, and it is another way of describing the necessary existent.

14 Al-Ġazālī, Tahāfut al-Falāsifa, p. 162.

15 Al-Ġazālī, al-Iqtiṣād fī al-Iʿtiqād, pp. 38–9.

16 Al-Ġazālī does not think that the philosophers are entitled to this claim. He challenges their arguments for the incorporeity of God in the Ninth Discussion of the Tahāfut.

17 Māhiyya is usually translated into ‘quiddity’ and ḏāt into ‘essence’. In Arabic texts the distinction is sometimes blurred, but the most consistent usage of these terms suggests that māhiyya is essence without the assumption of existence. (I'll have more to say about this later; see 15.)

18 Al-Ġazālī, Tahāfut al-Falāsifa, pp. 162–3.

19 These five types of plurality are the five forms alluded to in al-Ġazālī's transitional passage above. The descriptions of these five forms are given in the following five subarguments. (See al-Ġazālī, Tahāfut al-Falāsifa, pp. 163–4.)

20 Al-Ġazālī, Tahāfut al-Falāsifa, p. 163.

21 For example, in the Ninth Discussion he argues that the philosophers' arguments for the incorporeity of God are invalid.

22 Al-Ġazālī, Tahāfut al-Falāsifa, p. 163.

23 The Arabic word is maʿnā, which literally means “meaning.” The medieval Islamic philosophers and theologians use it frequently to mean “meaning,” concept,” “notion,” or even “thing.” Simon Van Den Bergh chooses ‘concept’ instead of ‘meaning’ in his translation of Ibn Rushd's (Averroes) Tahāfut al-Tahāfut (The Incoherence of the Incoherence), published by the Trustees of the “E. J. W. Gibb Memorial” (Cambridge, 1954), vol. I, pp. 175–6.

24 Otherwise, that clause makes little sense; for the philosophers and theologians agree that matter is a substance (ğawhar), and as such it is self-subsisting.

25 Al-Ġazālī, Tahāfut al-Falāsifa, p. 193.

26 Ibid., p. 163.

27 The Sixth Discussion of the Tahāfut is devoted to a critical analysis of the philosophers' arguments against the positive attributes. The reconstruction here is guided in part by that analysis.

28 This is assumed to be true because the positive attributes are supposed to be constitutive of the necessary existent's nature.

29 One might object here that the positive, divine attributes have necessary existence by virtue of their subsisting in the divine essence, and hence their necessary existence is not by virtue of themselves but by virtue of another. If this reasoning is correct, then the positive, divine attributes would not be necessary existents, in the technical sense of ‘necessary existent’ used here (see note 2). Although al-Ġazālī's passage cited above is silent about this point, I believe he would reject this reasoning. When we say that something has necessary existence by virtue of itself, we mean that its existence is necessary due to its own nature and not because it is a necessary effect of a necessary existent. The First Intellect, for example, is not necessary by virtue of its own nature (in fact, it is contingent when it is considered on its own) but rather it is necessary by virtue of being a necessary effect of God, who is the necessary existent. An attribute's nature is to subsist in an essence; hence the positive, divine attributes have necessary existence by virtue of their nature. Also, these attributes satisfy the other condition of a necessary existent – namely, being uncaused existents. In the passage that I cite below al-Ġazālī does indeed say that the difference between the divine essence and the divine attributes is that the essence is self-subsisting while the attributes subsist in the essence. For al-Ġazālī, this marks the distinction between the type of necessary existent that the divine essence is and the type of necessary existent that the divine attributes are, and this distinction is what permits one to maintain that God is one despite the presence of necessarily existing attributes, which subsist in the essence.

30 Al-Ġazālī, Tahāfut al-Falāsifa, pp. 172–3.

31 Ibid., p. 173.

32 In the original it is insāniyya, which means humanity or being human. But the context clearly implies that the correct phrase is ‘being rational’. I took the liberty of substituting ‘rational’ for ‘human’ to maintain the natural flow of the passage.

33 Al-Ġazālī, Tahāfut al-Falāsifa, p. 163.

34 Ibid., p. 185.

35 Ibid., p. 188.

36 Ibid., p. 187. ‘Agent’ is an unfortunate translation of the Arabic fāʿil. In the grammatical sense the fāʿil of a sentence is the subject of the verb, that is, the agent. The fāʿil in general is a doer, an active agent, someone or something that performs an action. There is a debate between the philosophers and al-Ġazalī whether agency in this sense requires will or not. The issue is important because the philosophers describe God as the agent (fāʿil) of the world, even though they believe that the world emanated from God by necessity. Al-Ġazālī thinks that calling an unwilling cause “agent” can only be metaphorical. According to him, agency requires will. Thus, he says in the Third Discussion of the Tahāfut that if someone threw another into a fire, then it is literally said that the man who threw the victim into the fire is the killer and it is only metaphorically said that the fire killed him. To this Ibn Rušd responds in Tahāfut al-Tahāfut that there is confusion here because the fire in this case is an instrument for the killing, but if the victim is burned without anyone throwing him into the fire, no one would say that the fire burned him metaphorically. (See Rushd, Ibn, Tahāfut al-Tahāfut, 4th edn, ed. Bouyges, Maurice [Beirut, 2003], p. 160.)Google Scholar

37 Al-Ġazālī, Tahāfut al-Falāsifa, pp. 185–6.

38 Ibid., p. 186.

39 Ibid., p. 164.

40 I am grateful to Roslyn Weiss for making this observation.

41 See note 3 for the distinction between temporal and essential causation.

42 Of course, arguments could be, and actually were, given to show that a necessary existent could not undergo change. In the language of the era, the necessary existent is devoid of occurrents (ḥawādiṯ). What is unclear is why this is assumed to be part of the essence of a necessary existent rather than a consequence of its essence.