The new video from indy100's favourite vloggers, ASAP Science, explains just what that means.
Some scientists believe that in 1,000 BCE, before we developed the concept of human consciousness, people assumed these voices were communication from the gods themselves. Things are very different now - research published by New York University in February found that at least 80 per cent of people hear a voice as they read.
But this process is very different for those with schizophrenia, ASAP Science explain
They're often associated with their current mental state and can be quite hostile, accusing threatening or persecuting. Ultimately embodying many of their fears.