(RNS) A teenager says God and Jesus appeared to him in a grove and told him to start a new Christian church. Another person claims the Almighty talks to him through the radio.

A French girl gets messages from heaven to lead an army against the British, while a Utah woman thinks she is meant to have Jesus' baby and 12 husbands.

Some of these figures were considered prophets and saints, while others were judged insane. The question is: How do you tell which is which?

Brian David Mitchell, convicted Friday (Dec. 10) of kidnapping and raping Elizabeth Smart, insisted that God gave him license to do so, though his attorneys argued he was mentally ill.

The main difference between a prophet and a psychopath, says Ralph Hood, who teaches psychology of religion at the University of Tennessee in Chattanooga, is "whether or not (they) can get followers."

Historic figures who started new religious movements -- including Martin Luther (the Reformation), Joseph Smith (Mormonism), Mary Baker Eddy (Christian Science), Ellen White (Seventh-day Adventism), Jim Jones (People's Temple) and David Koresh (Branch Davidians) -- were viewed by outsiders as delusional.

Peggy Fletcher Stack Peggy Fletcher Stack writes for the Salt Lake Tribune. See All Articles

But followers, ranging from the millions to the hundreds, found each of them to be credible guides to divinity.

"There is ample research to suggest that, for the most part, religious people are no more inclined to mental illness than nonreligious people," says Wendy Ulrich, a Mormon and founder of Sixteen Stones Center for Growth, a small group of mental-health professionals, in Alpine, Utah.

The pathology arises, Ulrich says, when a person's search for meaning "goes into extreme overdrive" and people "lose touch with vital aspects of reality."

From the start, psychologists must weigh a person's religious and cultural expectations. The more important faith is, the more prominent a role religious language will play in a person's mental process.

Maybe the person is speaking in tongues, communing with the dead, sensing the presence of a guardian angel or getting messages from milk cartons.

So the first question becomes: Does the experience fit with some religious tradition that is dominant in a culture? Does it make sense to a particular faith community, or is it out of the norm? Is it consistent with the faith's scripture, practices and beliefs or does it challenge them?

As a clinical psychologist, Brent Slife might bring in a pastor or priest to help answer that question.

"I would want to know how contextually appropriate their behavior or the things they are espousing are," says Slife, a Protestant who teaches at Brigham Young University. "Are they able to adapt to different contexts?"

Unbalanced people may repeatedly quote scriptures or obsessively perform rituals or adopt a grander, more spiritual identity such as King David, Moses, Muhammad or Jesus.

"If the pope says he's the Vicar of Christ, that's OK because it fits with a centuries-old tradition," Hood says. "If I think I am, I'm in trouble."

There are at least two common ways in which mental patients describe their delusional experiences with God, Ulrich says. Schizophrenics hear voices or see things that are not there. Those suffering from paranoia, meanwhile, see conspiracy in everyday events or think God is speaking specially to them.

"They over-interpret common experiences to mean either someone is out to get them or God is out to help them," Ulrich says. "Ideas of grandiosity and thinking of themselves as special or chosen in some way are not uncommon."

But it never is easy to assess the authenticity of another person's spiritual experience.

Ulrich has known people whose behavior could be inspiring or could signal a muddled mind. Many of them take part in church services without fellow believers even being aware.

She has known some religious folks who are unusually clairvoyant, with a penchant for and openness to revelatory experiences. They largely are calm, highly functioning, rational people, who are socially engaged but don't call attention to themselves.

"They pretty much play by the rules of society and don't think of themselves as special," she says. "They know their `gifts' are not always believed in or valued, so they have a sense of humor about them."

She's also seen people who are "very high-functioning in some areas of life and can be quite charismatic, intelligent and charming," but they begin to "over-interpret impressions or events as messages from God in ways that make other people nervous, even people within their own value system or religious system."

Such people think the "rules" of the community don't apply to them and may start to feel that others are out to get them, she says, and they don't understand why.

If you ask a religious person how God communicates, she might say through impressions or a kind of whispering. But if you ask a mentally ill person that question, he might say, "I shook hands with him yesterday."

Studies show that reasoning with schizophrenic patients about God never works, Measom says. They cannot be convinced of any other interpretation. It's a matter, he says, of core beliefs and brain chemistry.

For a believer such as the Rev. Gregory Johnson, the line between genuine religious experience and madness sometimes is blurred.

Johnson, who directs Standing Together, a Utah group of evangelical pastors, is not a charismatic Christian, so he doesn't speak in tongues or engage in the more ecstatic practices. But he does believe God heals, speaks and leads.

"I see a range of healthiness and levels of extremity within the confines (of Christianity)," he said. "I see people who are zealous but not insane."

One of the tests, Johnson says, might be the "fruits" or outcomes of the divine communication. Does the experience lead a person into more altruistic actions, greater caring for others and deeper relations, or does it simply draw the recipient further into narcissism?

As a pastor, Johnson says, he would worry about actions that are "destructive to other people or to themselves." Mormons are urged to seek and receive God's guidance for themselves and their families. But only the church's "prophet, seer and revelator" can receive messages for the whole faith and the world. Such institutional controls may inhibit individual experiences, but they do prevent mentally ill members from distracting or confusing the faithful.

Even as a young Mormon teen, Elizabeth Smart says she knew the difference between a genuine religious leader and Mitchell.

"God would never tell someone to kidnap a young girl from her family's home in the middle of the night from her bed that she shared with her sister ... and sexually abuse her and give her no free agency to choose what she did," Smart testified. "I know (Mitchell) was not called of God because God would never do something like that."