With this apostrophe the Savoyard Vicar addresses that human faculty which enables man to distinguish good from evil, which prohibits him from doing evil and makes him love the good.
Conscience is no more than reason applied to moral conduct in order to regulate it.
Just as our speculative knowledge derives from a few basic, immediately formed principles which enlighten it and guide it, so our moral judgements are derived from a few practical principles. The first of these principles is that we must do good and avoid evil. As soon as the human intelligence comes into contact with perceptible things, the conscience forms these principles. Created to know being, the intelligence immediately grasps the basic laws of what is and what should be. Thus it reveals its origin, since the absolute, universal and necessary character cannot come from itself but rather from a higher light which illumines it.