In the beginning I thought that it were people talking and me thinking that people said something while in reality they were not. Later I thought that I could induce the thoughts of others. Later I thought that people could also ventriloquize.
With time I took it for thoughts of others in such a way that it looked very much like telepathy.
Because I thought this unlikely I tried to convince myself that the only reasonable possibility, except for assuming it were my own thoughts, was that some electronic equipment was producing the voices: sound or some other stimulation of my hearing organs.
Later I returned again to the opinion that voices were the product of my brain: some kind of representation of the thoughts and speech of others; mainly because of some overvigilant searching for what others are saying and thinking, raising false alarm after little or nothing.