The central claim of deontologists is that certain types of act are intrinsically right or wrong, i.e. right or wrong in themselves, irrespective of their consequences.

This is in stark contrast to consequentialism, which holds that the moral status of an act is determined entirely by its consequences. Consequentialists hold that any act, even those acts that we would normally classify as morally wrong, is morally good if it has good consequences. In the view of the consequentialist, the end justified the means; it is morally permissible to use distasteful means (e.g. lying, stealing, physical violence, etc.) in order to achieve good ends (e.g. happiness, alleviation of suffering, etc.).

The deontologist is opposed to this approach; certain acts, the deontologist holds, should never be performed, even if performing them would lead to good consequences. This is the central thesis of deontology.

There are three main deontological theories: Kantian ethics, divine command theory, and agapism.

Kantian Ethics

The most famous deontologist is Immanuel Kant. Kantian ethics is firmly based in reason; we can derive moral laws from rational precepts, according to Kant, and anyone who behaves immorally also behaves irrationally. He stated the moral law thus derived in the form of the Categorical Imperative, which in many ways resembles the biblical injunction to “do unto others as you would that they should do unto you.”

Divine Command Theory

A second deontological theory is divine command theory. Divine command theory holds that God’s commands are the source of ethics, that God is a moral authority and we ought always to obey his commands, irrespective of the consequences of doing so.

Agapism

A further deontological ethical theory, also influenced by the Christian tradition, is agapism. Agapism, which derives its name from the Greek word “agape” meaning “love”, takes very seriously the great commandment of Mark 12:30-31: “you shall love the Lord your God with all your heart… you shall love your neighbour as yourself.” All of ethics, according to agapism, is summarised in this commandment. Agapism is a deontological system of ethics consisting of one simple command: in every situation, do the loving thing, whatever that may be.