“The Bible indicates that in our time the human race is divided in two. We all have sinned (Rom. 3:23); we have all rebelled against God. But some people—not all—have had their rebellious hearts changed and renewed, because God has worked in them to save them. They have trusted in Christ to save them from their sin, and have been united to him as their Savior. Within this life, they are not totally free from sin, but in their hearts they have turned to God and have begun to follow Christ (1 Thess. 1:9). Their minds are being renewed (Rom. 12:1–2).
As a result of this renewing work of God, there are two modes of thinking among human beings. There is rebellious thinking, and there is thinking in communion with God, that is, thinking that endeavors to have fellowship with God, to listen to him, and to submit to his instruction, relying on the power of the Holy Spirit. We might call these two kinds of thinking non-Christian thinking and Christian thinking. But the word Christian needs attention. Many people today may think of themselves as Christian because their parents were, or because they have feelings of admiration for Jesus, or because they attend services in a church building whose roots were Christian. All this is merely superficial. If Christianity is nothing more than this, it is fake Christianity. True Christianity is a matter of the heart, not a matter of a name.
We should also say that, historically, much evil has been done by people who claimed to be Christians. Some of them were only fake Christians. Others were genuine Christians but they nevertheless acted in accordance with sin that was still in them. Christians are not necessarily morally better than anyone else. In fact, they may be worse. But through the Holy Spirit they have recognized that they are worse and that they need help. They have come to Christ, and they have begun to change. But they may still have a long way to go. They may still commit terrible sins. Following the way of Christ does not imply that we condone evil deeds done in his name.
In short, even genuine Christians are not perfect in their deeds. Likewise, they are not perfect in their thoughts. Nevertheless, in principle there are two kinds of thinking, the Christian way and the non-Christian way. In terms of fundamental assumptions and commitments, these two ways are at odds with each other. They are antithetical to each other.
Because there are two kinds of thinking, rather than one, communication is a challenge. It is a challenge even when we study logic, because there are two ways of studying logic, the Christian way and the non-Christian way. The Christian way submits to God’s instruction through Christ. We can receive Christ’s instruction because God has caused it to be written down in the Bible. The non-Christian way follows other standards. Those standards may be the standards within some other religion. But most commonly they are standards of autonomy. Everyone simply judges for himself. As a result, we need to reckon with people’s allegiances and heart commitments. Within the twentieth century, some Christians have grappled with this difficulty, and presuppositional apologetics has arisen as a result. Because presuppositional apologetics aspires to be based on the Bible’s teaching, it disclaims any independent authority. It intends that its ideas and principles be based on the Bible. Presuppositional apologetics articulates how Christians may be fully loyal to Christ and to the Bible’s teaching when they engage in dialogue with non-Christians. We cannot expound presuppositional apologetics at length, so we will be content to summarize. Simply put, we who are followers of Christ must be consistent with our basic commitment to him. We submit to his instruction in the Bible. We sift human ideas using God as our standard. We know that God is the source of all truth. We know that even those in rebellion against him know him (Rom. 1:20–21) and rely on him (Acts 14:17). We can communicate with them because they are created in the image of God and live in his world. We can talk about any subject we choose, because every area of life reflects God’s presence in the world. We may speak about what the Bible says, because the Bible as God’s word has spiritual power to convict listeners, even when they do not yet agree that it is God’s word (1 Cor. 2:1–5).
But in our communication with non-Christians we try to make it clear that we do not agree with their fundamental assumptions and fundamental commitments against God. We have presuppositions different from theirs.
Because of God’s mercy, non-Christians can know and do know many bits of truth. In fact, they know God (Rom. 1:20–21). But Christians and non- Christians see truth differently, because non-Christians suppress the fact that they are receiving truth from God, and that what they know is found first of all in the mind of God.
These principles apply to the study of logic. We will try to study logic as followers of Christ. In the process, we need to acknowledge that our thinking is distinct from the thinking of non-Christians. We may still invite non-Christians to listen to our thinking. But the issues are clearer if they are aware that Christians and non-Christians have differing presuppositions.”
(Poythress, Logic, 41-43)