Although they were not together, the cosmological argument of Al Farabi and Avicenna is close enough that there is no need for a separate post for each one.
I. "What it is" vs "That it is"
Consider the definition of something. A dog. A dog is a carnivorous mammal with four legs, a tail, and a snout. But just from knowing what it is, we cannot tell that it is. I.e., that it exists. We have to go out into the world to see if dogs actually exist:
Or consider the Higgs boson. This is the elusive particle that physicists were looking for using large particle accelerators or "atom smashers." They knew that the Higgs boson had certain properties, such as a specific charge and spin. But they did not know whether it existed, and for this reason built atom smashers such as the Large Hadron Collider. Again, we could know what a Higgs boson is but just from that not know that it exists.
So for most objects of our experience, their definition, or essence, does not entail their existence. In other words, these objects are not the source of their own ongoing existence. So since their ongoing existence does not come from themselves, it must come from outside them. In other words, they must be dependent on other factors for their existence. For example, a lake does not entail its own existence; its existence is maintained by warm air, gravity, and so forth. But these factors also do not entail their own existence, and we see that warm air depends on a source of heat, and gravity depends on mass, and a source of heat depends on nuclear reactions, and so on.
This leads into a regress…
II. Dependent Objects Imply an Independent Object
What kind of regress are we talking about, here? We don't mean a regress stretching back in time, but rather a hierarchical regress of dependent members here and now:
If object A does not entail its own, ongoing, existence, then it must depend on other factors for its own ongoing existence, as we saw. But the same applies to those other factors. Now consider a chain of clamps that only stay closed if held by another clamp:
The only way this chain of clamps will stay closed if there is at least one "permanent" clamp holding shut one of the clamps, which then in turn holds together the rest of the clamps. One clamp must be "independent": not held shut by any further clamps:
Similarly, if object A is receiving or dependent on further factors for its ongoing existence, and those factors are themselves dependent upon further factors, then this must terminate in something not dependent upon any further factors:
To put it another way, all these objects whose essence (what it is) is separate from their existence (that it is) must trace to something whose essence is its own existence. That is to say, existence itself.
III. Existence Itself = God?
Now that we have arrived at the conclusion, existence itself, what must this thing be like? It must be eternal, as existence cannot not exist. It must be immutable, as nothing cannot exist and so existence must always exist. It must be unchangeable, because change entails a gain of something that was lacking, and a lack of something is the non-existence of something, and existence itself cannot have non-existence. It cannot be material, or have spacial location, or exist in time, because all these things entail change. It must have all positive properties to a maximum degree, because anything less than maximum would entail a lack of something, which is non existence. This would entail such properties as maximum power, maximum knowledge, and maximum goodness: