The consciousness humans have that an action is morally required or forbidden. In the Christian tradition the nature of this awareness and its status as knowledge is a central problem. On the one hand it is sinful to act against one’s conscience; on the other hand conscience can deceive, since we can be mistaken about what is required or forbidden. Aquinas puts the problem thus: ‘if obeying and disobeying a mistaken conscience are both bad, it seems that men with mistaken consciences are caught in a trap, and cannot avoid sin’ (Summa Theologiae, IaIIae 19.6). The solution is to distinguish between errors of conscience that are voluntary or blameworthy and ones that are involuntary: in the former case we are responsible, in the latter we only do wrong unknowingly. The problem of the authority of conscience became urgent with the rise of Protestant ethics, in which it plays the role hitherto reserved for the independent authority of the Church. Critics of the notion include La Mettrie and Nietzsche, both of whom regarded a bad conscience as a kind of malady.