Lesson 7: The Argument of Possibility and Necessity

The argument of possibility (imkān) and necessity (wujūb) which is sometimes briefly described as the argument of possibility is one of the most solid rational arguments to prove the existence of God. This argument occupies a sublime station among the Muslim philosophers, being mentioned as the way of the philosophers in proving the existence of God. The lucid assertion of this argument is traceable to Ibn Sīnā (died 437 AH) and through him it has also found its way into the Christian theology.

One of the arguments of Thomas Aquinas (died 1274), the famous Christian theologian, is the argument of possibility and necessity. He has learned this argument from Mūsā ibn Maymūn1 (died 1204), the Jewish theologian, who, in turn, has learned it from Ibn Sīnā. The firmness of this argument has led Muḥaqqiq al-Ṭūsī to rely on it mostly in his book Tajrīd al-Aqā’id in proving the existence of God. In his words,

اَلمَوْجودُ إنْ كانَ واجِباً فَهُوَ الْمَطْلوبُ، وَإلاّ اِسْتَلزَمَهُ دَفْعاً لِلدَّوْرِ وَالتَّسَلْسُلِ.

That is to say, “If the existent (to whose existence there is no doubt) is the Necessary Being (wajib al-wujūd) by essence, our object of desire (maṭlūb) is proved to be real. And if it is not so, it necessitates the existence of the Necessary Being by essence so as not to require a vicious cycle of definitions or arguments.

The Argument’s Premises

1. That there is a reality out there is not something imaginary or illusionary. There is no doubt about it. Denial of this fact will be nothing except sophistry, and by accepting sophistry, there will be no way for any discussion or discourse and there will be no room for proving or negating the existence of God.

2. That which has reality and existence is rationally either of the two possibilities. One is that its reality and existence is identical with its essence and in its reality, it does not depend or need anybody or anything else (the Necessary Being by essence). Another possibility is that in its reality and existence, it is in need of another existent (Possible Being by essence). The first possibility is what is claimed by the theists who regard God, the Exalted, as its manifestation, and this is what the argument of possibility and necessity seeks to prove.

3. An existent which is in need of another existent in its reality and existence is an effect and the existence of an effect without the existence of its cause is impossible. Therefore, the existence of effect necessitates the existence of its cause.

4. The existence of cause is either the Necessary Being by essence or the Possible Being by essence. In the first case, it is sought after, proved and attained, and in the second case, the existence of a cause is an effect of another existent.

5. If an existent whose cause is its effect is the very effect, a vicious cycle of arguments is inevitable. That is, a thing is the cause as well as the effect of another thing. There is no doubt that the cause comes first before the effect. A thing thus comes before (for being the cause) as well as after (for being an effect) another thing. This coming before (taqaddum) and after (ta’akhkhar) also exists in a thing; that is its very existence. As a result, there arises a contradiction which is essentially and axiomatically impossible.

In other words, the effect of the effect of a thing is its effect, just as the cause of the cause of a thing is its cause. Here, A is the effect of B and B is the effect of A. Therefore, A is the effect of A; that is, the existence of A comes before (for being the cause) as well as after (for being an effect) its essence, and it is a clear contradiction [of thinking].

6. If an existent whose cause is another existent other than the effect and this existent is an effect of yet another existent, and this process continues ad infinitum such that it does not end in the Existent that is not an effect, this necessitates the existence of an unbroken chain of cause and effect which is rationally impossible likewise.

7. This is because in this case, all existents are possible beings and are in need [of causes prior to their existence], and on the other hand, the existent in need [of a prior cause] will not exist without another existent which gives existence to it.

8. Therefore, the concomitance of circular argument is that no existent will come into being and this is false and contrary to the first premise. And if we consider their existence incontrovertible and at the same time deny the existence of their cause, we have actually denied the principle of causation.

The assumption of an unbroken chain of cause and effect is like the case of infinite lamps that have spontaneously acquired light from nowhere; that is an effect without a cause.

From the above assertion, it becomes clear that the argument of possibility and necessity is a rational analysis and synthesis about reality and existence, and its point of beginning is the acceptance of the principle that reality (wāqi‘iyyah) can be divided into two, viz. necessary (wājib) and possible (mumkin). And in both cases, the object of desire (wājib al-wujūd bi ’dh-dhāt or the Necessary Being by essence) can be proved [to be logically true].

In the first argument, therefore, the states and attributes of the existents, through whose contingency, order and movement the existence of God is asserted, are not examined. It is true that the attribute of ‘possibility’ (imkān) is also mentioned in this argument, but this attribute, like the attribute of ‘necessity’ (wujūb), is attained through rational analysis and not through sensory observation and pondering over natural creatures. For this reason, Ṣadr al-Muta’allihīn has said:

“If the theosophers had not also observed the existence of the tangible world, their belief concerning the existence of God, His Attributes and all His Actions would have been different from their existing belief.”2

Bertrand Russell’s Misgiving

In his book Why Am I Not a Christian? Bertrand Russell says:

“The first rational argument in proving [the truth of] the existence of God is that everything that we can see in the world has a cause, and no matter how long this chain of causes takes, it must end up in the First Cause and finally this First Cause shall be called ‘God’.”

In criticizing this argument, he then says:

“If every thing must have a cause or reason, then the existence of God must have also a cause or reason, and if there is a thing which can exist without a cause or reason, disputing about the existence of God will be useless because the existence of nature is also possible without a cause.”3


The reply to this misgiving is clear, provided that we acknowledge the value of reason in judging theoretical disputes, because in its rulings and judgments, reason follows fixed and categorical criteria and standards, and it will never issue a definite judgment unconscionably or on the basis of untenable criteria. The criterion of the dictate of reason regarding causation – that is, an existent’s need for a cause – is that the existent is in a situation when existence and non-existence are equal in terms of its essence.

The assumption of the emergence of such an existent without the existence of a cause is tantamount to contradiction; that is, it has both existence and non-existence. If the negation and affirmation of both are equal as far as its essence is concerned, then there is contradiction. The solution to this contradiction is for us to say that it has existence on account of something outside its essence; hence, it is in need of another (i.e. cause).

Any existent in which this criterion exists is in need of a cause – whether it is material or not material, essential or accidental, objective or subjective, etc. On the contrary, any Existent in which this criterion cannot be found in the sense that existence and non-existence are not the same as far as Its essence is concerned, and in fact, existence and necessity are identical with Its essence and reality, then any talk about causation with respect to It is irrational and inconsequential.

Meanwhile, as to whether such a Reality exists or not, the answer is affirmative, and the reason for this is the very argument of necessity and possibility and the impossibility of circular proof. Without this Reality, the world of being cannot be rationally explained and interpreted. That is, negation of the Necessary Being by essence necessitates negation of the principle of reality and existence (including the necessary and possible), and in clearer terms, negation of the Necessary Being by essence is tantamount to the negation of the existence of God.

It is necessary to point out here that what is meant by ‘explaining’ and ‘interpreting’ the world on the basis of the belief in the Necessary Being by essence has nothing to do with the way these two words (‘explain’ and ‘interpret’) are construed in scientific hypotheses. Interpreting natural facts and events on the basis of hypotheses will never arrive at the logical certainty, because the correctness of hypothesis cannot be established by logical analysis and rational argument; rather, the way of proving it is sensory experimentation and experience, and in view of the limitations of the empirical method, the possibility of contrary result cannot be totally ruled out. However, explaining the world on the basis of the existence of the Necessary Being by essence can be realized through logical analysis and rational argument which are anchored in the principle of non-contradiction.

In clearer terms, by assuming that heat is not the cause of expansion of metals, no contradiction necessarily arises, but to assume that there is no Necessary Being by essence in the chain of existence, this is tantamount to contradiction.

In principle, if every thing is supposed to be in need of an explanation and anything which has no explanation is not correct, then one can ask Mr. Russell, for example, “Why did you pick up the book from the library’s bookshelf?” One of his probable answers is this: “I wanted to read it.” And if he would be asked why he wanted to ready it, his answer might be: “This is because I consider reading useful and interesting.”

If he would be asked, “Why do you desire for anything which is useful and interesting?” most probably he could not give any answer to this question. In this case, based on his notion that anything which cannot be explained is not correct, it necessarily follows that he must deny himself because he cannot explain the fact that he wants to do anything which is useful and good.4

Review Questions

1. Briefly state the argument of possibility and necessity along with its six premises.

2. State and refute Bertrand Russell’s objection to the argument of possibility and necessity.

3. Write briefly the historical background of the argument of possibility and necessity.

4. State briefly the assertion of the argument of possibility and necessity.

5. What conclusion can be drawn from the argument of possibility and necessity?

  • 1. Mūsā ibn Maymūn (1153-1204): the Qurtubā (Cordova)-born well-known Jewish philosopher, theologian and physician who moved to Morocco and Palestine and finally settled in Cairo, Egypt, where he became a physician in the court of Sulṭān Ṣalāḥ al-Dīn and the leader of the Jewish community there. His major works in medicine and philosophy were written in Arabic and his 14-volume magnus opus in theology remains a major source of Jewish theology and law to this day. [Trans.]
  • 2. Ṣadr al-Muta’allihīn, Sharḥ al-Hidāyat al-Athīriyyah, p. 283.
  • 3. Bertrand Russell, Why Am I Not a Christian, trans. S.A.S. Ṭāhirī, p. 19.
  • 4. This argument is made by ‘Allāmah Muḥammad Taqī Ja‘farī in his book Barguzīdeh-ye Afkār-e Russell (A Selection of Russell’s Ideas), p. 71.