Islamic philosophy makes a sharp distinction between different categories of believers. Some, and indeed most, believers follow Islam in an unquestioning and natural manner. They adhere to the legal requirements of the religion, carry out the basic rules concerning worship, pilgrimage, charity and so on, and generally behave as orthodox and devout Muslims. Some are more devout than others, and some occasionally behave in ways reprehensible to the teachings of Islam, but on the whole for the ordinary believer Islam presents no serious theoretical problems. There may well be practical problems in reconciling what they wish to do with what Islam instructs them to do, but this for most people is not something which leads them to question their faith as such. It merely leads them to wonder how to reconcile in a practical way the rival demands of religion and their personal wishes.

This category of ordinary believer is very different from the kind of believer who has difficulty in formulating his or her faith in terms which are satisfying to them intellectually as well as practically. Such ‘seekers after truth’ can follow a number of specifically Islamic routes to try to resolve their difficulties. They may work within the Islamic sciences such as jurisprudence (fiqh), law (sharī'a) or the rather more controversial discipline of theology (kalām). What all these activities share is an acceptance of the basic principles of Islam, which are employed as the basic principles of each individual discipline.