Answering Presuppositionalism: Extra Credit
Presupposition lists hold that a theistic worldview is the only one that can account for knowledge. In particular, they claim that atheists cannot justify their use of inductive reasoning, while God provides a firm epistemological basis; in other words, a firm foundation for knowledge. The uniformity of nature—of the UN, as it's often abbreviated—is the name given to the apparent consistency of the universe's physical laws over space and time. Without uniformity of nature, the universe would be a chaotic place where the past wouldn't resemble the future.
To use inductive reasoning is to make an estimate of how likely a general statement is to be true based on specific knowledge. Inductive reasoning is used when trying to predict future events from knowledge of the past. In a universe without uniformity of nature, where the past didn't resemble the future at all, inductive reasoning would be useless. Presuppositionalists say that God guarantees the uniformity of nature and, in doing so, provides justification for inductive reasoning.
Vantil, one of the most well-known presuppositionalists, said the existence of the God of Christian theism and the conception of his counsel as controlling all things in the universe is the only presupposition which can account for the uniformity of nature that the scientist needs. When Vantil says that the uniformity of nature needs accounting for, he is assuming that a chaotic universe is more likely than a uniform one and that a God is necessary to provide uniformity. But since Vantil has never seen a universe other than the one we all live in, this is an unfounded assumption.
For all we know, it may not be possible for a Godless universe to be anything but uniform. Far from the Christian God being the only presupposition that can account for the uniformity of nature, it's one of many. There are an infinite number of unlikely-sounding assumptions that can account for the uniformity of nature, such as the Flying Spaghetti Monster or other guarantees of the uniformity of nature. There are also some far more parsimonious presuppositions; perhaps the simplest one is that uniformity of nature is true.
Presuppositionalists think they have a firm foundation for knowledge that the rest of us lack. Here they are making a double error, because, as well as mistakenly believing that the uniformity of nature needs accounting for, they seem to believe that the uniformity of nature is sufficient to provide a rational basis for inductive reasoning when it isn't. Even in a universe with uniformity, inductive reasoning can never be epistemologically justified.
Just because the pen dropped to the floor yesterday doesn't mean that a previously unknown universal law will prevent it from falling to the ground today. To demonstrate that the atheist has no basis for assuming the validity of inductive reasoning, the presuppositionalist asks how we can know that the universe will continue to be uniform. If the answer involves appealing to knowledge of the past, then it uses induction to try to validate induction, which is begging the question.
The presuppositionalist mistakenly thinks he has a solution to this problem through revelation. God lets him know that the universe will continue to be uniform. But how can he be sure that God won't change his mind about uniformity? The presuppositionalist might cite God's unchanging nature as a guarantee that he won't change his mind. But what grounds does a Christian have to conclude that God's nature is, in fact, unchanging and that it will continue to be so?
Whether you gain knowledge of God's unchanging nature through direct revelation or through scripture, the only way he can say anything about God's nature in the future is to use induction. Appealing to God to solve the problem of induction merely postpones the point at which induction has to be invoked to justify itself, thereby begging the question. Presuppositionalists can't rationally justify their use of induction any more than the rest of us can.