In Stages of Faith (1981), James Fowler attempted to lay out a developmental process for human faith. His stages parallel other attempts to explain developmental processes in other areas, like Piaget's theory of cognitive development and Kohlberg's stages of moral development.
Like Piaget and Kohlberg, Fowler hypothesized that as human beings grow and develop physically, cognitively, and emotionally, our ability to think, reason, and develop morals and faith change as well.
Fowler outlined six stages of faith development:
Intuitive-Projective: Fantasy and reality are often mixed together. Many preschool-age children inhabit this stage. The ideas we pick up about God and faith at this stage, however, often shape our approach to faith for the rest of our lives.
Mythic-Literal: Stories related to one's faith tradition are interpreted literally, even if the person understands other aspects of their lives in a non-literal way. Many school-age children inhabit this stage; some people stay here their entire lives.
Synthetic-Conventional: As one's social circles expand, so does one's quest for a belief system that ties them all together. Teenagers are often in this stage, as they start to understand themselves as occupying different personas in different social circles. Those that don't see they are "inside" a belief system, however, may develop a lifelong sense of rigidity, trusting only certain authorities (like a spiritual leader or a particular text).
Individuative-Reflective: Here, one begins to understand that their faith perspective is only one of many. They may become disillusioned with their former faith and seek to understand others' faith perspectives. Many people who reach this stage do so in young adulthood, as their understanding of others' perspectives expands.
Conjunctive Faith: At this point, one realizes that not all human experiences can be explained by logic. They begin to make or find room in their faith for paradoxes and mystery. Often, they're interested in sacred myths and symbols, though not in the literal or rigid way they may have been as children. While most people do not reach this stage, those that do most often encounter it in mid-life, when they have time and perspective to reflect on their own and others' existence.
Universalizing Faith: Most people never reach this stage. Those that do, however, tend to live their faith rather than discuss or question it. They express few worries or doubts, seeing love and justice as universal principles.
One strength I see in Fowler's system is that it can help clarify why people behave as they do in regards to faith. For instance, many young adults start seeking to learn more about other faith perspectives, only to find that their family or the community they've grown up in accuses them of "losing faith" or "backsliding."
In fact, Fowler argues, this attempt to explore other perspectives is an attempt to engage in a newly meaningful way about faith—one that fits the other developmental experiences in a young adult's life, such as leaving home and learning that other people have different perspectives on politics, music, sports, or how to clean a house.
One weakness is see is a weakness that appears in many attempts to describe developmental stages. In an attempt to clarify the development of faith, Fowler's system also oversimplifies it to some degree. These stages are dependent to an extent on one's life following a "typical" developmental structure.
In reality, humans are messy. We have conflicting needs and desires, and we can bounce around these various stages in various ways. For instance, a young adult who abandons their childhood faith in favor of a new one (stage 4) may dive headfirst into their new faith, taking all its stories literally (stage 2) and fiercely defending its leadership and ideals against any attempts to question them (stage 3). While Fowler's framework can be a guide, it should not be taken as gospel.