My proposal, therefore, for a consistently Christian methodology of apologetics is this:
1. That we use the same principle in apologetics that we use in theology: the self-attesting, self-explanatory Christ of Scripture.
2. That we no longer make an appeal to “common notions” which Christian and non-Christian agree on, but to the “common ground” which they actually have because man and his world are what Scripture says they are.
3. That we appeal to man as man, God’s image. We do so only if we set the non-Christian principle of the rational autonomy of man against the Christian principle of the dependence of man’s knowledge on God’s knowledge as revealed in the person and by the Spirit of Christ.
4. That we claim, therefore, that Christianity alone is reasonable for men to hold. It is wholly irrational to hold any other position than that of Christianity. Christianity alone does not slay reason on the altar of “chance.”
5. That we argue, therefore, by “presupposition.” The Christian, as did Tertullian, must contest the very principles of his opponent’s position. The only “proof” of the Christian position is that unless its truth is presupposed there is no possibility of “proving” anything at all. The actual state of affairs as preached by Christianity is the necessary foundation of “proof” itself.
6. That we preach with the understanding that the acceptance of the Christ of Scripture by sinners who, being alienated from God, seek to flee his face, comes about when the Holy Spirit, in the presence of inescapably clear evidence, opens their eyes so that they see things as they truly are.
7. That we present the message and evidence for the Christian position as clearly as possible, knowing that because man is what the Christian says he is, the non-Christian will be able to understand in an intellectual sense the issues involved. In so doing, we shall, to a large extent, be telling him what he “already knows” but seeks to suppress. This “reminding” process provides a fertile ground for the Holy Spirit, who in sovereign grace may grant the non-Christian repentance so that he may know him who is life eternal.
– Cornelius Van Til, My Credo (Jerusalem and Athens) p.20-21