From his origin, man's being resonates with some things and clashes with others. This anamnesis is not a store of retrievable contents, but an innate capacity to recall what is in accord with what man's nature seeks. We don't have arguments to prove it's there, but it just is there. Ratzinger prefers this recalling. Conscience according to Saint Thomas is not a faculty or a habit but an act.
Conscience is the application of our reason to a concrete situation.
It is an act of the practical reason which applies a knowledge to a particular situation. Practical reason begins with the spark of synderesis and utilizing the light it receives from education and the instinctive moral law, and taking into account the concrete situation, the conscience makes a judgment about an action to be undertaken, or a judgment about an act that has already been done. Even though conscience is not a habit, but it is formed by habits, the virtues of wisdom, knowledge, and prudence and by supernatural virtues. Conscience is an act of reason, not of appetition, which means that conscience belongs to the order of cognition and not feeling. We mentioned that in a healthy person the emotions support the judgment of conscience, that the emotions are well-integrated with reason.