Christian apologists such as Gary Habermas have argued that the hallucination theory is not plausible. The primary argument given by Habermas and other defenders of the resurrection against the theory is that hallucinations are experienced by individuals not groups. Since the NT records Jesus appearing to groups of people at various times, those appearances cannot be hallucinations. Habermas poses the following question: If, as most psychologists assert, hallucinations are private, individual events, then how could groups share exactly the same subjective visual perception?
First, and most importantly, Habermas is presupposing that the accounts in the NT are true in every detail. The school where he teaches, Jerry Falwell's Liberty University, has in its doctrinal statement the following: We affirm that the Bible, both Old and New Testaments, though written by men, was supernaturally inspired by God so that all its words are the written true revelation of God; it is therefore inerrant (emphasis added) in the originals and authoritative in all matters. If one begins by assuming that the gospels are without error, then of course one is going to conclude that Jesus arose literally from the tomb. One is going to find it impossible to explain what is recorded in the NT on a purely naturalistic basis if one begins with the prior faith commitment that the Scriptures are absolute truth. But that is simply begging the question.
Second, one could theorize that perhaps Peter was the first to have a vision of Jesus and then as he told the other disciples about his experience, some of them also had a similar experience. It is not necessary to suppose that they all had the same experience at the same time unless one presupposes the inerrancy of the gospels. The same holds true of the 500 to whom Jesus is said to have appeared. Since Paul give no details about the alleged appearance--not the time, not the place, not the circumstances, not the names of the people involved, nothing--then, it is impossible to evaluate the claim.
Third, contrary to Habermas' claim, it is possible for a group of people to hallucinate at the same time. Hallucinate may not technically be the best word to describe group appearances, but regardless, we know that groups of people have all claimed to see the same apparition at the same time. The best examples are the cases of Marian apparitions which have occurred throughout history and today in settings where groups of people claim to have seen the Virgin. In recent times, these group visions of Mary have taken place in Conyers, Georgia and Medjugorje, Bosnia.
The Skeptic's Dictionary defines collective hallucination as:
a sensory hallucination induced by the power of suggestion to a group of people. It generally occurs in heightened emotional situations, especially among the religiously devoted. The expectancy and hope of bearing witness to a miracle, combined with long hours of staring at an object or place, makes certain religious persons susceptible to seeing such things as weeping statues, moving icons and holy portraits, or the Virgin Mary in the clouds.
Those witnessing a "miracle" agree in their hallucinatory accounts because they have the same preconceptions and expectations. Furthermore, dissimilar accounts converge towards harmony as time passes and the accounts get retold. Those who see nothing extraordinary and admit it are dismissed as not having faith. Some, no doubt, see nothing but "rather than admit they failed...would imitate the lead given by those who did, and subsequently believe that they had in fact observed what they had originally only pretended to observe...."(Rawcliffe, 114).
Not all collective hallucinations are religious, of course. In 1897, Edmund Parish reported of shipmates who had shared a ghostly vision of their cook who had died a few days earlier. The sailors not only saw the ghost, but distinctly saw him walking on the water with his familiar and recognizable limp. Their ghost turned out to be a "piece of wreck, rocked up and down by the waves" (Parish, 311; cited in Rawcliffe, 115).
The Rawcliffe cited above is the psychologist, Donovan H. Rawcliffe, who in 1952 wrote a book entitled: Illusions and Delusions of the Supernatural and the Occult . On page 113 of that book, he writes:
The same factors which operate for a single individual in the induction of hallucinations or pseudo-hallucinations may become even more effective in an excited or expectant crowd, and on occasion may result in mass hallucinations. This is not to say that any two people are capable of having precisely the same hallucination identical in every respect. But similar preconceptions and expectations can undoubtedly result in hallucinatory visions so alike that subsequent comparisons would not disclose any major discrepancy. . . . Accounts of comparatively dissimilar hallucinatory experiences often attain a spurious similarity by a process of harmonisation in subsequent recollection and conversation.
Since we know that the reports of the post-mortem appearances of Jesus were passed down by oral tradition for many years before they were ever recorded, it is quite reasonable to assume that the various accounts were harmonized as they were retold.
Habermas is right to argue that its impossible for a group of people to have precisely the same hallucination at the same time but its not necessary to believe that is what actually occurred unless one presupposes the inerrancy of the written gospels. Thus, Habermas dismissal of the hallucination theory on the grounds that mass hallucinations is impossible is misguided.