Psychologist and philosopher William James described four characteristics of mystical experience in The Varieties of Religious Experience. According to James, such an experience is:
- Transient – the experience is temporary; the individual soon returns to a "normal" frame of mind. Feels outside normal perception of space and time.
- Ineffable – the experience cannot be adequately put into words.
- Noetic – the individual feels that he or she has learned something valuable from the experience. Feels to have gained knowledge that is normally hidden from human understanding.
- Passive – the experience happens to the individual, largely without conscious control. Although there are activities, such as meditation (see below), that can make religious experience more likely, it is not something that can be turned on and off at will.
Norman Habel defines religious experiences as the structured way in which a believer enters into a relationship with, or gains an awareness of, the sacred within the context of a particular religious tradition (Habel, O'Donoghue and Maddox: 1993). Religious experiences are by their very nature preternatural; that is, out of the ordinary or beyond the natural order of things. They may be difficult to distinguish observationally from psychopathological states such as psychoses or other forms of altered awareness (Charlesworth: 1988). Not all preternatural experiences are considered to be religious experiences. Following Habel's definition, psychopathological states or drug-induced states of awareness are not considered to be religious experiences because they are mostly not performed within the context of a particular religious tradition.
Moore and Habel identify two classes of religious experiences: the immediate and the mediated religious experience (Moore and Habel: 1982).
- Mediated – In the mediated experience, the believer experiences the sacred through mediators such as rituals, special persons, religious groups, totemic objects or the natural world (Habel et al.: 1993).
- Immediate – The immediate experience comes to the believer without any intervening agency or mediator. The deity or divine is experienced directly.
In his book Faith and Reason, the philosopher Richard Swinburne formulated five categories into which all religious experiences fall:
- Public – a believer 'sees God's hand at work', whereas other explanations are possible e.g. looking at a beautiful sunset
- Public – an unusual event that breaches natural law e.g. walking on water
- Private – describable using normal language e.g. Jacob's vision of a ladder
- Private – indescribable using normal language, usually a mystical experience e.g. "white did not cease to be white, nor black cease to be black, but black became white and white became black."
- Private – a non-specific, general feeling of God working in one's life.
Swinburne also suggested two principles for the assessment of religious experiences:
- Principle of Credulity – with the absence of any reason to disbelieve it, one should accept what appears to be true e.g. if one sees someone walking on water, one should believe that it is occurring.
- Principle of Testimony – with the absence of any reason to disbelieve them, one should accept that eyewitnesses or believers are telling the truth when they testify about religious experiences.
The German thinker Rudolf Otto (1869–1937) argues that there is one common factor to all religious experience, independent of the cultural background. In his book The Idea of the Holy (1923) he identifies this factor as the numinous. The "numinous" experience has two aspects:
- mysterium tremendum, which is the tendency to invoke fear and trembling;
- mysterium fascinans, the tendency to attract, fascinate and compel.
The numinous experience also has a personal quality to it, in that the person feels to be in communion with a holy other. Otto sees the numinous as the only possible religious experience. He states: "There is no religion in which it [the numinous] does not live as the real innermost core and without it no religion would be worthy of the name" (Otto: 1972). Otto does not take any other kind of religious experience such as ecstasy and enthusiasm seriously and is of the opinion that they belong to the 'vestibule of religion'.