Ibn Sina (Avicenna):

Al-isharat wa al-tanbihat

Is there anything that necessarily exists?

Background

Ibn Sina's book Al-isharat wa al-tanbihat (the book of remarks and admonitions [warnings]) is about the nature of logic and philosophy. He wrote the book especially for philosophers and so it's quite tricky. One of the most famous parts of the book is an ingenious attempt to prove the existence of God.

The proof of the truthful

Ibn Sina says that there are two kinds of proofs of God - one is based only on the concept of existence itself, and the other requires thinking about God’s creation and God’s acts.

According to Ibn Sina, the former kind of proof is nobler - it is the proof of ‘the truthful’.

The proof relies on a distinction between things that necessarily exist and things that only possibly exist. If it relies on something else for its existence then its existence is possible. My cup of coffee only possibly exists because it wouldn’t have existed if I didn’t make it, for example.

Part I: the cause of all possible things

Everything that exists has either necessary existence, or possible existence.
For a group of possible things, either
- It causes itself and is therefore necessary—but this isn’t possible because a group of possible things must itself also be possible.
- The cause is the totality of the group—but this doesn’t make sense because the totality of the group is the same as all its members - which are possible.
- The cause of the group is some of its members—but this doesn’t make sense because no member of the group is caused any more or less than the others.
- The cause of the group is external to the group.
∴ Every group of possible things requires a cause external to the group.

Chapter 9. Admonition: The Necessary in itself and the Possible in itself

Every being, if considered from the point of view of its essence and without consideration of other things, is found to be such that either existence necessarily belongs to it in itself or it does not. If existence belongs to it necessarily, then it is the truth in itself and that whose existence is necessary from itself. This is the Independent Reality… [E]very existent either has necessary existence in essence or has possible existence in essence.

—Fourth Class, ch. 9

...the existence of every possible thing is from another.

—Fourth class, ch. 10

Every totality having every one of its units as caused requires a cause external to its units. This is because either

it does not require a cause at all; hence it is necessary and not possible. But how could this be so when it is only necessitated by its units?
It requires a cause that is all its units; hence it is caused by itself. That totality and all [its units] are one thing…
It requires a cause that is some of its units. But if every one of its units is caused, then some of its units are not more deserving of being the cause than some others. The reason is that the cause of the caused is more deserving of being the cause. Or
it requires a cause external to all its units. This is the remaining [truth].

—Fourth class, ch. 12

It’s true that the group of possible things might be caused by something itself which is possible, but then that possible thing must be caused by something else and so on… if that chain includes a necessary thing, then that necessary thing must be the first cause.

… if this chain includes an uncaused thing, then this thing is an extremity and a limit. Therefore every chain terminates in that whose existence is necessary in itself.

—Fourth class, ch. 15

Part II: the oneness of the necessary thing

The necessary thing is defined by its necessity or by something else.
If it is defined by something else, then it depends upon something else for that quality.
If this is true then that quality is possible and not necessary.
If this is true then the thing itself is possible/caused.
∴ The necessary thing must be defined by its necessity and nothing else.
∴ every necessary thing is exactly the same.
∴ There can only be one necessary thing.

Chapter 18. remark: Proof for the Unity of the Necessary in Existence

That whose existence is necessary is something specific. If its specificity is due to the fact that it is that whose existence is necessary, then there is nothing else whose existence is necessary. If, on the other hand, its specificity is not due to this but to something else, then it is caused.

—Fourth class, ch. 18

This conclusion was particularly important in Islam. The doctrine of the oneness of God is called Tawhid. It is implied in the Shahadah, 'There is no God but God'.

Tasks

Explain the difference between something that has necessary existence and something that has possible existence.
Explain why, according to Ibn Sina, every group of possible things requires a cause external to the group.
Explain why, according to Ibn Sina, there can only be one necessary thing.
Explain an objection to Ibn Sina's argument
Do you find his argument convincing? Explain your answer.

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