One of the principal aims of Kant’s Metaphysics of Morals, especially of the Doctrine of Virtue, is to present a taxonomy of our duties as human beings. The basic division of duties is between juridical duties and ethical duties, which determines the division of the Metaphysics of Morals into the Doctrine of Right and the Doctrine of Virtue. Juridical duties are duties that may be coercively enforced from outside the agent, as by the civil or criminal laws, or other social pressures. Ethical duties must not be externally enforced (to do so violates the right of the person coerced). Instead, the subject herself, through her own reason and the feelings and motives arising a priori from her rational capacities -- the feelings of respect, conscience, moral feeling and love of other human beings, must constrain herself to follow them (MS 6:399-404). Among ethical duties, the fundamental division is between duties to oneself and duties to others.
Within each of these two main divisions of ethical duty, there is a further division between duties that are strictly owed, requiring specific actions or omissions, and whose violation incurs moral blame, and duties that are wide or meritorious, the specific actions not strictly owed, but deserving of moral credit or merit. Kant treats these latter as ‘duties’ (eschewing any category such as ‘supererogation’) because the actions in question are conceived as fit objects of self-constraint – things we can make ourselves do through the exercise of reason and the moral feelings arising from the application of practical reason to our faculty of desire. Regarding duties to oneself, this division is between ‘perfect’ and ‘imperfect’ duty; regarding duties to others, the strict or narrow duties are called ‘duties of respect’ while the wide or meritorious ones are called ‘duties of love.’
We may represent the major divisions of Kant’s system of duties in the following diagram: