Opinions about mechanisms of psi are wide-ranging. Because the field is multidisciplinary, there are physical theories, psychological theories, psychophysical theories, sociological theories, and combinations of these.

On one end of the spectrum, the "physicalists" tend to believe that the "psi sensing capacity" is like any other human sensory system, and as such it will most likely be explained by known principles from biophysics, chemistry, and cognitive science. For these theorists, psi is expected to be accommodated into the existing scientific structure, with perhaps some modifications or extensions.

On the other end of the spectrum, the "mentalists" assert that reality would not exist if it were not for human consciousness. For these theorists, the nature of the universe is much more effervescent, thus accommodating psi into existing scientific models will require significant modification of science as we know it. Strong theoretical debates are common in parapsychology in part because spirit, religion, the meaning of life, and other philosophical conundrums commingle with quantum mechanics, probability theory, and neurons.

Some theorists have attempted to link psi phenomena with similar- sounding concepts from quantum mechanics, including non-locality, instantaneous correlations at a distance, and other anomalies. Such suggestions always spark vigorous debates, and at some point it seems the critics are inevitably accused of not properly understanding quantum mechanics. (This is why we do not discuss quantum mechanical theories of psi here. See, however, the Mind-Matter Unification Project at Cambridge University.)