In this crazy book written, as we'll see, to prove that its author was not crazy, Donnelly proposes an explanation of spiritualist and allied phenomena that is - as far as I know - wholly unique and original. His unprecedented idea is that every time we meet someone, we create a kind of phantom clone of them:
... when two human beings meet and exchange mutual recognition through the senses, their intelligences unconsciously beget outside their bodies living, perfect spirit copies of each other, which reproduce in spirit form their prototypes' physical form and mental attainments. This power of begetting subjective concepts of humans is enjoyed by the personality from infancy until death. These subjective concepts of humans constitute the spirit world and the only spirit world man has ever known.
Moreover like Swift's fleas, each copy has lesser ones to bite 'em:
In the concept I took of Mr. Doe, there is a concept-copy, not only of me, but of each human being with whom Mr. Doe has exchanged recognition. These concept-copies surround my concept of Mr. Doe, just as the concepts begotten by the personality of Mr. Doe surrounded Mr. Doe's body.
Thus Donnelly's theory violates Occam's Razor in a most outrageously literal fashion by absolutely insisting on the multiplication of entities.
So what do these “subjective concepts” actually do? Most of the time not much, as they are a state of sleep, “held in abeyance by the rapport between the percipient and the concept-copies owned by his concepts of humans” - whatever that means. On the other hand:
If [a person's] concepts are ever awake, it is while he is asleep. Their wakefulness must come from some foreign influence, such as the concentrated thought about him, entertained by an absent friend. If the friend, just as he is about to pass into sleep, thinks intently about the absent friend and harbors the wish to be with him, this thought would be grasped by his concepts he has of the absent one, now at the threshold of consciousness, and when he passed into sleep would carry out his wish and visit the absent friend.
The presence of the visiting concepts would awaken the concepts of acquaintances, owned by the visited, and would carry to the owner, the percipient, in a dream something relating to the absent friend. It is in this way that the vast majority of dreams are produced.
So when I dream about taking an exam at school without my trousers on, it's because an old friend of mine who was also in that exam room has been thinking about me at bedtime (though if that is the case the trouserlessness is made slightly worrying). On the other hand, presumably those with no friends rarely have dreams at all. But dreams, significant as they are, are only a small part of the role played by “subjective concepts”, which are also behind spiritualistic phenomena such as table-tilting and automatic writing, as well as certain stage illusions:
During January, 1918, Houdini, on the Hippodrome stage in New York City, night after night, before an audience of thousands, at the wave of his wand caused an elephant to vanish instantly. Houdini himself does not make it vanish. What does? The vast army of invisibles over which Houdini has control. He knows nothing about subjective concepts and believes the disembodied spirits at his suggestion render invisible the twenty thousand pound pachyderm.
Most experts contend that Houdini, who was notably a lifelong sceptic, employed large mirrors rather than disembodied spirits when performing this trick - but there's always room for doubt.
Though he is keen to show how his theory explains the workings of mediums and psychics in general Donnelly's central concern is with what he calls “clairaudience”. This word is usually defined to mean a form of extra-sensory perception but it becomes clear that what Donnelly refers to is something more uncontrolled: the experience of auditory hallucinations, or in common language, “hearing voices”.
What is the meaning of clairaudience or subjective hearing? It means that the clairaudient hears distinctly his subjective concepts of humans, begotten by his Personality, addressing him subjectively. No one else present hears them. His Personality has, unknown to him, begotten subjective concepts, living facsimiles of all human beings he has met and with whom he has exchanged recognition. These subjective concepts are outside the percipients body, and when by some stress placed upon the Personality, it awakens them, they speak just as their Prototypes would. But, since they are subjective, their mental voice is heard by no one but their owner, the percipient.
Since clairaudience is caused by subjective concepts - which everyone has though few can hear them - it should therefore not be taken as an axiomatic symptom of mental illness:
Now all clairaudients whose brain matter is normal and whose only trouble comes from their awakened subjective concepts of humans, are not proper subjects to be treated by materialistic doctors who deny the existence of a spirit world.
This class constitutes, I believe, over eighty per cent of clairaudients. These, if they only knew the source of the subjective voices would be as competent to care for themselves and earn their own living as any normal man. They are not insane, but abnormal.
[...] if you [the American people] continue to permit materialistic doctors to consign your relatives and friends to the insane asylum, because they claim to hear voices from the unseen, the time will come when the taxes for the care of the clairaudient men and women now cruelly and unjustly confined in insane asylums will become oppressive and legislative measures will be adopted to lessen them.
If the present legally empowered doctors, who know nothing about the clairaudient's condition, are continued as judges of all abnormals, the only course by which oppressive taxes can be avoided is by passing the innocent clairaudient for all time through the peaceful path of euthanasia.
In plain words, the innocent clairaudient will be done to death by law!
The reason for Donnelly's interest in this subject, notwithstanding aside his impassioned plea against undue deaths and taxes, was that he himself heard voices:
I am thirty-eight years clairaudient and for thirty-six years I have held responsible positions and acquitted myself as well as I did when normal.
Happily, nowadays it is recognised that - in the absence of other symptoms - auditory hallucinations are not sufficient evidence of madness, even when the sufferer adopts crackpot theories to explain them. Donnelly was almost certainly not mad, though ironically he'd have seemed more sane if he hadn't written this very long-winded and deeply weird book to prove himself so.
In the final section of the book, entitled “the Islander”, Donnelly rashly attempts to bring his theory to life through the means of a fictional story, about one “Patrick O'Donnell” - an orphan left alone on a desert island until discovered and brought back to civilization by a Catholic missionary - and his various experiences with fever, hypnosis and other phenomena that Donnelly wanted to illustrate. In the course of his account Patrick's subjective concepts are allowed to speak for themselves, in as vivid a manner as you might expect:
My prototype was the first human being Patrick met. I am the first human subjective concept his Personality took. He was then about twenty-two years old. For nearly two years after I was begotten I was unconscious of my existence, because Patrick was normal. When Patrick had typhoid fever the heat of his body expelled the Personality. I remember seeing him out of his body, but I was confused and knew nothing about my condition. Patrick's Personality was confused even more than I, for it could not think and reason while out of its home, the brain, while I, in spirit form, had a perfect spirit brain, and could reason as well as could my Prototype.
(And the moral of this tale is, of course: don't mess with spirits, they can get you out of your brain.)