Others have argued: that natural evils are the result of the fall of man, which corrupted the perfect world created by God that forces of nature are neither "goods" nor "evils". They just are. Nature produces actions vital to some forms of life and lethal to others. Other life forms cause diseases, but for the disease, hosts provide food, shelter and a place to reproduce which are necessary things for life and are not by their nature evil. that natural evils are the result of natural laws Williams points out that all the natural laws are necessary for life, and even death and natural disaster are necessary aspects of a developing universe. that natural evils provide us with a knowledge of evil which makes our free choices more significant than they would otherwise be, and so our free will more valuable or that natural evils are a mechanism of divine punishment for moral evils that humans have committed, and so the natural evil is justified. Free will defense The problem of evil is sometimes explained as a consequence of free will. Free will is a source of both good and of evil, since with free will comes the potential for abuse. People with free will make their own decisions to do wrong, states Gregory Boyd, and it is they who make that choice, not God. Further, the free will argument asserts that it would be logically inconsistent for God to prevent evil by coercion because then human will would no longer be free. The key assumption underlying the free-will defense is that a world containing creatures who are significantly free is innately more valuable than one containing no free creatures. The sort of virtues and values that freedom makes possible – such as trust, love, charity, sympathy, tolerance, loyalty, kindness, forgiveness and friendship – are virtues that cannot exist as they are currently known and experienced without the freedom to choose them or not choose them. Augustine proffered a theodicy of freewill in the fourth century, but the contemporary version is best represented by Alvin Plantinga. Plantinga offers a free will defense, instead of a theodicy, that began as a response to three assertions raised by J. L. Mackie. First, Mackie asserts "there is no possible world" in which the "essential" theistic beliefs Mackie describes can all be true. Either believers retain a set of inconsistent beliefs, or believers can