Rationalism has been vigorous in modern western ethics, from British moralists of the eighteenth century to Kant and his disciples, then to more recent intuitionists such as Moore and Ross. The common elements have been the beliefs that the values of acts and intentions to which we refer by words such as ‘good’ and ‘obligation’ are objective or factual, but in some sense ‘non-natural’, and that they are recognizable by intellectual acts which are different in kind from those by which we recognize characters of sense data or our own mental states. From this brief description we can see that modern rationalism has followed roughly the tradition of Aristotelian ethics. No doubt one could trace its lineage through medieval Christian theories of natural law.

In classical Islam also the existence of rationalist ethics has long been familiar to scholars in the Muʿtazilite theology, with its insistence on the objective nature of good and evil, justice and injustice. Here it was not opposed to naturalistic ethics, as in the modern West, but to the voluntaristic theory developed by the Ashʿarites out of Shafiʿite jurisprudence: the definition of value in action as obedience to divine commands, and the consequent impossibility of knowing right and wrong except from revelation or something dependent on it in one way or another – Traditions, analogy, consensus of the ʿulamāʾ. Ashʿarite ethics have always been well known through the works of Ghazālī, Shahrastānī and others.