In this book, Phillip Wiebe examines religious, spiritual, and mystical experiences, assessing how these experiences appear to implicate a spiritual order. Despite the current prevalence of naturalism and atheism, he argues that experiences purporting to have a religious or spiritual significance deserve close empirical investigation. Wiebe surveys the broad scope of religious experience and considers different types of evidence that might give rise to a belief in phenomena such as spirits, paranormal events, God, and an afterlife. He demonstrates that there are different explanations and interpretations of religious experiences, both because they are typically personal accounts, and they suggest a reality that is often unobservable. Wiebe also addresses how to evaluate evidence for theories that postulate unobservables in general, and a Theory of Spirits in particular. Calling for more rigorous investigation of these phenomena, Wiebe frames the study of religious experience among other accepted social sciences that seek to understand religion.
Weibe, in his final work, approaches the question of the reality of "spirits" - mostly focusing on case studies of exemplary instances of visions and contacts with apparitions and other manifestations. Much of his data come from a Christian context, and Weibe is open about his own commitment to Christianity so while this makes sense, it also keeps the work from being more broadly comparative, although certain comparisons are made between say the resurrection of Jesus and Yogananda's and his own guru's visions of their gurus after their deaths. He attempts to base his own "Theory of Spirits" on logically consistent reasoning, invoking C.S. Pierce's notion of abduction or hypothesizing based on observable data, as well as comparisons to various scientific enterprises which posit the existence of unobservable "theoretical objects" such as certain sub-atomic particles of theoretical physics visible only in terms of their aftereffects. For spirits, we have the data of RSM ("religious-spiritual-mystical") experiences, which are quite considerable. Sadly, Weibe doesn't seem to be too familiar with the extensive literature on altered states (Tart, Kripner, etc.) or comparative mysticism (Richard Jones, McGuinn, Underhill, etc.), but even with the data he has gathered himself in terms of the experiences of friends, acquaintances, and in the literature and newspapers - as well as his own experience of possession and self-exorcism - he makes a strong case for the consideration of these experiences as ontologically significant and worthy of study. They are significant both for our understanding of reality as such, as well as integral to the continued plausibility of religion generally.