The term 'adiaphora' (plural of the Greek adiaphoron) denotes things or acts that are indifferent. It was used by the Cynics and later by the Stoics. Althogh early Christians considered several matters to be morally or religiously indifferent, 'adiaphora' was not applied to Christian liberty in the NT, but was first used by the church fathers. The presumption about adiaphora differs greatly, some holding that what is not specifically allowed by scripture is prohibited, others holding that what is not expressly prohibited by scripture is permitted. For the Reformer John Calvin (Institutes 3.19.7-12), there are three parts of Christian liberty, freedom from law righteousness, willful and joyful obedience to God's will, and freedom to use or not to use outward things that are themselves 'indifferent'. But following Paul (1 Cor. 10:23-24), Calvin notes that 'nothing is plainer than this rule: that we should use our freedom if it results in the edification of our neighbor, but if it does not help our neighbor, then we should forego it.'

In a 16th-century controversy, the Adiaphorists were Melanchthon's followers who held that some Catholic practices, such as the veneration of saints, were 'adiaphora' and could be accepted for the sake of peace and order, while others repudiated them as a restoration of 'popery'. In the second Adiaphoristic controversy, in the 17th century, the Pietists held that secular amusements, such as the opera, were excluded by the Christian life, while their opponents contended that they were adiaphora, or indifferent matters. Schleiermacher later rejected the concept of adiaphora in view of the unity and continuity of Christian life, but also held that ordinary, secular amusements could be oligatory as well as permissible.

Emphasising that 'the life of the Chirstian is a whole, and ... is not composed of different isolated segments,' Emil Brunner (The Divine Imperative, ET 1937) contends that 'both these statements are true: there are no 'Adiaphora,' and- everything is 'adiaphoron'- save love. Dilige et fac quod vis (love, and do what you will- Augustine.' Everything is neutral, and yet everything is connected with the whole which God dircts. Thus, 'there are no moral holidays.'

Most ethical theories concentrate on the determination of obligatory and prohibited, right and wrong, actions, sometimes also identifying praiseworthy actions, such as works of supererogation. Even if they do not explicitly identify and specify indifferent acts, they recognise them, at least implicitly. Such acts are optional and are thus within the agent's discretion, as long as they do not harm, injure, or offend others.