In Acts 14:17, Paul tells his pagan audience that although, in times past, God allowed all nations to walk in their own ways, nevertheless He did not leave Himself without witness. As the context makes clear, Paul is speaking in this passage not of human testimony, but of testimony built into the very pattern of Providence and the structure of Creation. There seem, in fact, to be at least four such witnesses to His reality and moral requirements, and Scripture attests to all four of them. Despite all our evasions and self-deceptions, these witnesses cannot be silenced. Just as they spoke to the people of Paul’s day despite the wickedness of his times, so they speak to the people of our day despite the wickedness of ours.Conscience is the first and most fundamental of these witnesses. As the same apostle wrote in Romans 2:14-15 (NIV), “Indeed, when Gentiles, who do not have the law [of Moses], do by nature things required by the law, they are a law for themselves, even though they do not have the law, since they show that the requirements of the law are written on their hearts, their consciences also bearing witness.” However, the term ‘conscience’ may be used in two different senses. Philosophers and theologians have traditionally distinguished these senses by the terms conscientia and synderesis (rel. to NT syneidesis), but we may call them “surface conscience” and “deep conscience.”Synderesis or deep conscience is that feature of the created human intellect that is designed by God to bear witness to the most general and foundational precepts of good and evil. It is not acquired through moral instruction; on the contrary, unless it was there already, such instruction would be gibberish to us. In other words, the function of moral teaching and nurture is not to “pump in” the basic distinctions between good and evil and between right and wrong (which would be impossible), but to elicit, sharpen, and reinforce our latent knowledge, to embed it in practices and virtues, to arm it with the developed power of judgment, and to protect it from misapplication.Conscientia or surface conscience is the application of moral knowledge to the individual case; we may also think of it as conscious moral belief, especially about the details of moral law. Although surface conscience is derived from deep conscience, this fact must not be understood to mean that it is always derived correctly and honestly. Indeed surface conscience can go deeply wrong, either through ignorance of fact, error in reasoning, or obstinate self-deception. Thus, when natural law thinkers speak of the ‘formation of conscience,’ they mean the formation of surface conscience.The purpose of this talk is to explore the foundations of conscience, and especially – considering the evils that are blithely proposed in our day – to discuss what happens when we suppress it: When we tell ourselves that we don’t know what we really do.