Presuppositionalists are famous for their Transcendental Argument for the Existence of God (TAG). This is the argument that attempts to prove God's existence by arguing that logic, morals, and science ultimately presuppose the Christian worldview, and that God's absolute nature is the source of logic and morals. The presuppositionalist maintains that the unbeliever "borrows" the truths of the Christian worldview, the existence of logic, the existence of morality and the ability to reason from the Christian worldview. They hold that these "truths" cannot be derived from the nontheistic worldview. The nontheistic worldview, they claim, has no basis to believe that the chance arrangement of atoms has produced a reliable basis for thinking (reason and logic) or for morality. These things are only possible if they come from outside of nature, i.e., a transcendent being.
An interesting dialogue took place on this issue between Douglas Wilson and Farrell Till. It was printed in Credenda/Agenda (Vol. 7; No. 1) under the title, "Justifying Non-Christian Objections."
Below is some of the interchange with my comments in bold.
DW: Many unbelievers commonly object to the God of the Bible on the basis of ethical "problems" with the character of God as revealed in the Scriptures. Whether they use psalms of imprecation, the slaughter of the Canaanites, the eternal wrath of God on the impenitent, etc ., the central theme is usually the same "Who would want to worship a God like that !" But despite the surface plausibility of the objection, a careful examination of it shows their Achilles attacking our Hector with his bare heel. Far from being the unbeliever's strongest case against the true God, this objection actually reveals the radical futility of unbelief; without God there are no ethical objections to anything.
FT: Although you didn't expressly state the "objective-morality" position of evangelical apologists, you certainly implied it when you said that "without God there are no ethical objections to anything." The fallacy of this position is its failure to recognize that morality is an intellectual abstraction. As such, it is no different from abstractions of tragedy, sorrow, or any of many other abstractions the human mind has formulated from its broad range of experience. Arguing that human intelligence cannot determine if acts are immoral without a god to tell us they are is as illogical as arguing that we cannot tell if events are tragic without a god of tragedy to tell us they are.
Wilson states: without God there are no ethical objections to anything.
Besides the fact this is an assertion not an argument, it does not agree with our experience and our knowledge of the world. People all over the world have beliefs about what is right or wrong and many of these people do not believe in a transcendent being. For example, there are nearly 1 billion Buddhists in the world, there are millions of atheists and agnostics. If only those who are "true Christians" as Wilson would define them have a true knowledge of this transcendent being, then that would mean well over 95% of the people on the earth don't recognize the true God and yet they all have a theory of ethics that they live by.
Where did man get this system of morality? Wilson would say that it is derived as a result of man being made in the image of God. I would dispute this on the basis that man's moral intuitions tell him that it is wrong to slaughter babies, yet the God whose morality we are supposed to reflect, ordered the massacre of babies in the OT on multiple occasions. Man's moral intuitions also tell him that it is wrong to punish an innocent person in place of the guilty person, yet God's plan of atonement is based on this very principle. How can man, on the one hand, have this sense of morality as a result of being made in the image of God and, on the other hand, God's actions betray this sense of morality?
So if man's sense of morality does not come from God from where does it come? I think it comes as a part of man's evolutionary development. Why do all men have a similar sense of basic right and wrong? Because we all are descended from common ancestors. We share the same human nature. It is as natural for man to have a common sense of right and wrong as it is natural for all men to walk upright. Why are there some differences among men as to the details of morality? I think its due to the fact that man lives in groups and these groups (societies) have over the years established laws based on what seemed to be the most advantageous for the betterment of the group. In many cases, these same "laws" would not apply to "outsiders." Outsiders could be treated in a way that would be wrong to treat insiders. Nevertheless when man thinks abstractly, he typically thinks of "laws" that should be applicable in every case to every man. This doesn't come, in my opinion, from a transcendent being but rather comes from man's ability to think abstractly and universally.
DW: Fine, I'll bite. If there is no God, then all the things you mention are in the same meaningless category. Morality, tragedy, and sorrow are equally evanescent. They are all empty sensations created by the chemical reactions of the brain, in turn created by too much pizza the night before. If there is no God, then all abstractions are chemical epiphenomena, like swamp gas over fetid water. This means that we have no reason for assigning truth and falsity to the chemical fizz we call reasoning or right and wrong to the irrational reaction we call morality. If no God, mankind is a set of bi-pedal carbon units of mostly water. And nothing else.
FT: You bit too hard. In equating all human abstractions with "swamp gas over fetid water," you overlook verifiable facts. The human mind can think; swamp gas can't. Human intelligence can evaluate situations and formulate abstractions of beauty, happiness, sorrow, fairness and morality; swamp gas can't. Are these abstractions valid? Well, what IQ level is needed to conceptualize abstractions like beautiful, sad, fair, right or wrong? Can one with an IQ of 100 do it, or must his IQ be infinite? The existence of moral concepts is verifiable; the existence of gods who put such concepts into human minds is unverifiable. Please address this problem.
DW says: Morality, tragedy, and sorrow . . . are all empty sensations created by the chemical reactions of the brain . . . If there is no God, then all abstractions are chemical epiphenomena.
Wilson is confusing the mechanical or chemical operations of the brain with what the brain produces. The operations of a computer could be described based on the electrical activity within the circuit boards, etc. but that would not discredit the data that is derived from this electrical activity working within silicon chips. If one wants to argue, "Yes but the computer was designed and if evolution is true, the brain was not," that is another issue altogether. We would now be moving to the teleological argument for the existence of God. There are answers to this argument but it would take us away from the argument from morality put forward by Wilson.
DW: You missed my challenge. You acknowledge the distinction between human intelligence and swamp gas, but you have no way to account for it. If there is no God, then why is there a distinction between the chemical reactions in your head and elsewhere? Suppose we agreed that the walls of a house are straight. I say there must be a foundation under it -- a precondition for straight walls. Your hypothesis is the house has no foundation at all and doesn't need one. "See, the walls are straight without a foundation." But given your worldview's assumptions, why ? Can you explain how time and chance acting on matter can produce the straight walls of reason and morality?
FT: No, you missed my challenge. You are the asserter, so you must bear the burden of proving your assertion. You have asserted that "without God there are no ethical objections to anything," so I insist that you prove that. You have admitted that human intelligence can formulate abstractions, but you say that " all abstractions are chemical epiphenomena, like swamp gas over fetid water." Prove that please. Can the brain's solution of algebra problems be right? If so, does "God" have to put the right solutions into the brain? If not, can a brain that correctly solves algebra problems correctly solve moral problems? If not, why not? Where did your god get his intelligence?
Wilson does move to the teleological argument and insists that without God, one could not account for how man's mind works. I think this is a failure on Wilson's part to understand evolution. Man's mind has evolved over thousands of years by adapting to its environment. Those adaptations that were useful for man's survival have been passed along whereas those that were not, have not been passed down. Since man is adapting to his environment it appears that there may be some design involved but this is only apparent not real.
DW: "There is truth in the theism-atheism controversy." Amen. You are able to say so because you assume that truth is objective. Again, you bet. But objective truth cannot be validly derived from the premises of your worldview. You are borrowing objective rationality and morality from the Christian worldview in order to attack the rationality and morality of the Christian worldview. There was a moral problem in the Amalekite attack -- Saul was disobedient and didn't kill everything as God instructed. You should have no objection. Given your worldview, there is no moral difference between the Amalekite massacre and a day at the beach. In both cases, all you have is atoms banging around.
FT: If the Amalekite children who were killed with Israelite spears could speak, would they say there was any difference in what happened to them and a day at the beach? You know they would. What IQ level would they need to distinguish the difference? You have evaded the issue long enough, so why don't you tell us how much intelligence is needed to formulate abstractions of beauty, loyalty, justice, etc.? Without a god of beauty, can one validly determine that a sunset is beautiful? If so, why can't one determine that acts are immoral without a god of morality? Truth is objective because of reality, not because some deity arbitrarily decides what truth is.
I tend to disagree that there is absolute objective morality or absolute objective rationality. I think that since all men are subjects and all the knowledge we have we received as subjects, that there is no way for any of us to speak in terms of the "truly objective." We can come to an agreement on what appears to be the case and this is about as close to objectivity as we can get. For example, how do we know that an apple is red? We "know" because we have come to an agreement on what "red" looks like. There is basic and universal agreement on the color "red." However, there are various shades of red and once we get outside of the basic color red we may no longer agree on whether a particular shade of red is truly red. So, in essence the identification of "red" is subjective but because we have come to universal agreement on at least one shade of "red," we can all agree that an apple is red. The same is true of language. The only reason we can communicate with one another is because we have agreed on what certain combinations of letters mean. There is basic agreement but once again it can break down based on the subjectivity involved (i.e., one's interpretation of the words).
DW: If morality is not objective, then it is subjective. If it is subjective, then it is as diverse as five billion subjective states of mind. Such fragmented subjectivity provides no authoritative ethical voice, and hence no morality deserving of the name. Related to this, you must now disclaim "objective rationality" as well as "objective morality," for the two are built on the same foundation -- or rather, in your worldview, not built on the same non-foundation. But if objective rationality does not exist, then your worldview does not permit you to reason for three words in a row, much less 115. The laws of logic are as nonmaterial as the God you so diligently oppose.
FT: Are you arguing that subjectivism cannot determine truth? If so, reality will not support your claim. You keep harping about my worldview, so please address the many problems in your "worldview." Where did "objective" reality come from? From God? Well, where did he come from? How can one determine what "objective" morality is? From the Bible? If so, a lot of subjectivism will be involved in reading and interpreting it. Looking for "objective" morality in the Bible will produce a morality "as diverse as 5 billion subjective states of mind." If not, why not? "Such fragmented subjectivity" will provide "no authoritative ethical voice" and so "no morality deserving of the name." Please address this issue.
When Wilson says that without God and objective morality, we will have 5 billion different views of what is moral, he fails to consider two things: 1) As stated above, all men share a common ancestry and our brains have evolved in the same way--thus we think similarly. Wilson's view could only be maintained if we all evolved separately on different planets and then were brought here to earth to form a society. Then, we would all think differently. 2) Morality is "objective" in the sense that men agree together on what they consider to be right and wrong within their social group. Just as red is "objective" in the sense that we have agreed on its basic color.
While the transcendental argument for God might seem convincing at first glance, once one "drills down" into the argument, it is found to be hollow (see these articles) It is really quite ludicrous to think that man can only have a sense of right and wrong if God exists and he can only know what is right and wrong if God tells him in a holy book.