This chapter begins with an etymological and historical elucidation of the terms conscientia and synderesis. Philosophical and theological reflection on these terms, beginning with St. Jerome and proceeding through thinkers such as Peter Lombard and Philip the Chancellor, constitutes the background against which St. Thomas Aquinas develops his understanding, not only of conscientia and synderesis, but also of objective right (ius) or rights. Much of the debate regarding synderesis, the infallible basis of conscientia, concerns whether it is a power or habitus. Aquinas settles on understanding synderesis as a ‘habit’ of the potential intellect – which, following Aristotle, he understands as a sort of ‘blank slate’ upon which things can be written. One of the things written on the habit of synderesis is the practical version of the principle of non-contradiction: ‘good is to be done and pursued, evil avoided’. This allows him to develop a theory according to which objective rights are primary, although not to the exclusion of subjective rights. It also allows those in agreement with Aquinas to exclude subjective rights that contradict established objective rights.

Some find the theology of an eternal punishment to be morally repugnant and theologically without warrant. But even if such is true of traditional doctrines of Hell, typified by those of Aquinas, it is not implausible to read Inferno as an “anti-narrative,” among other reasons because the literatures that write of a truly infernal mentality – for example,that of Dr. Faustus in Marlowe’s play – are vastly significant and their significance would not be lost even were Hell as an eternal condition impossible. For an infernal will is psychologically possible, even if the Hell willed is impossible as an existent state of affairs.

Cajetan Cuddy looks at conscience through the thought of St. Thomas Aquinas. Conscience is an act of ordering knowledge – some universal and some particular – to an act, whether past, present, or future. Conscience directs future acts, and regarding past acts, can accuse or excuse. Aquinas compares conscience and synderesis – the person’s inclination shaping her understanding. Synderesis turns human nature to good and objects to evil. It gives awareness of the principles of morality to be applied to actions. Synderesis concerns knowing the principles applicable to all actions, and conscience applies knowledge to a specific act. Thus, conscience comes from synderesis. But conscience has limits and can be wrong and need correction. A mistaken conscience does not stop a person’s orientation to the truth, and error can be fixed. Conscience and God’s law both bind for Aquinas, not because conscience is perfect or reason is independent of the law, but because conscience mediates God’s norms to humans doing a particular action. This is done through the application of synderesis, which is always ordered to moral truth, meaning to God.