In order for conscience to be consistently and absolutely reliable, infallible, it must stem from an infallible source - God. Alternatively, conscience might have a potential of ultimate reliability, if the faculty of conscience was dynamic and capable of solving problems i.e. if it was an innate part of human nature. St.Paul, Newman, Aquinas, Butler and Freud all argue on their ideas of what the conscience is and how reliable it can be towards ethical decision making.
St.Paul’s argument for the conscience can be found in the New Testament where the Greek word used for conscience is synderesis. This is the pain suffered by the one who goes against his or her moral principle. In Romans 2:15 Paul described the conscience as the witness to the requirements of the law being written on the hearts of those who are not under the law. In other words the conscience acts as a guide even where specific moral principles are not taken into consideration. It can be argued that St Paul’s conscience theory can be followed regardless of religious beliefs. However, some people may argue that St Paul’s idea of the conscience is undeveloped. There is no evidence to back up what he is saying as any reference to the conscience in the bible can only be referred to St Paul’s biblical writings. Therefore, we cannot say the conscience is a reliable guide to ethical decision making as there is no evidence to back up what St.Paul argues.
St Thomas Aquinas believed that the conscience was a device or faculty for distinguishing right from wrong through use of reason. He believed that it is a natural part of mental activity and provides an individual with moral guidance. He argued that there are two parts to making a moral decision; the Synderesis, this is the right reason, the awareness of being able to do good and prevent evil and the Conscienta, it distinguishes between right and wrong applies this