C. S. Lewis Natural Law Argument for God (Mere Christianity)
1. Good and Evil exist
2. Humans are capable of distinguishing the two
3. something must exist to make good, good, else bad and good would merely be two opposing forces neither better or worse than the other
4. because good is better than evil, a god does exist
Note: this is a extreme simplification of a great read, this also only proves the existence of a power which has the ability to determine morality or lack thereof