The preservation argument, also known as the conservation of existence argument, was proposed by René Descartes in his Meditations on First Philosophy. It is based on the alleged need for an explanation for why an individual continues to exist from moment to moment. After rejecting non-divine causes, he concludes God exists. This is a variant of the first cause argument.
The argument runs: 
- Something other than me causes the continuation of my existence (since I did not create myself from nothing).
- The cause must be a thinking being because the cause cannot be lesser than the effect.
- Any cause that is not divine lacks the attributes necessary for its own preservation.
- There cannot be an infinite regress of causes.
- Therefore, God exists.
- "But perhaps the being upon whom I am dependent is not God, and I have been produced either by my parents, or by some causes less perfect than Deity. This cannot be: for, as I before said, it is perfectly evident that there must at least be as much reality in the cause as in its effect; and accordingly, since I am a thinking thing and possess in myself an idea of God, whatever in the end be the cause of my existence, it must of necessity be admitted that it is likewise a thinking being, and that it possesses in itself the idea and all the perfections I attribute to Deity. "
Preservation is equivalent to creation
Descartes considers preservation as something only a divine agent could achieve because it is equivalent to creation ex nihilo.
- "In truth, it is perfectly clear and evident to all who will attentively consider the nature of duration, that the conservation of a substance, in each moment of its duration, requires the same power and act that would be necessary to create it, supposing it were not yet in existence; so that it is manifestly a dictate of the natural light that conservation and creation differ merely in respect of our mode of thinking [and not in reality]. "
No self preservation
Descartes gives various reasons why he could not preserve himself: 
- Only divine agents could preserve things, and humans do not have divine powers.
- If I preserve myself, I could be aware of that fact.
Apart from suffering the same problems as the first cause argument, it also has some distinctive issues.
Do things that exist need preservation?
The argument assumes that existent objects need a cause to remain in existence. This is contrary to common experience in which an object that has nothing acting upon it remains static and unchanged. It is perfectly conceivable that objects preserve themselves even if they are not aware of it, despite Descartes' assertion to the contrary.
Since no reason is given for the requirement for a cause of preservation, it is an unsupported premise.
The equivalence of preservation and creation is not well supported. It is only an analogy.
Perhaps natural laws make objects remain in existence. If apologists ask for a cause of the natural laws, the argument becomes the natural-law argument.
Assertion that non-divine objects cannot be self-preserving
The assertion that non-divine objects cannot be self-preserving is another unsupported premise. Descartes claims that there must be "at least be as much reality in the cause as in its effect" is also unsupported. How does one go about deciding what has more or less "reality"?