A neurosurgeon once told me about operating on the brain of a young man with epilepsy. As is customary in this kind of operation, the patient was wid… - Daniel Dennett

[T]he Capgras delusion [is] a bizarre affliction that occasionally strikes human beings who have suffered brain damage. The defining mark of the Capgras delusion is the sufferer's conviction that a close acquaintance (usually a loved one) has been replaced by an impostor who looks like (and sounds like, and acts like) the genuine companion, who has mysteriously disappeared! … What is particularly surprising about these cases is that they don't depend on subtle disguises and fleeting glimpses. On the contrary, the delusion persists even when the target individual is closely scrutinized by the [Capgras sufferer], and is even pleading for recognition. Capgras sufferers have been known to murder their spouses, so sure are they that these look-alike interlopers are trying to step into their shoes — into whole lives — that are not rightfully theirs! There can be no doubt that in such a sad case, the [sufferer] in question has deemed true some very specific proposition of nonidentity: This man is not my husband; this man is a qualitatively similar to my husband as ever can be, and yet he is not my husband. Of particular interest to us is the fact that people suffering from such a delusion can be quite unable to say why they are so sure.

[I]n all mammalian species that have so far been carefully studied, the rate at which their members engage in the killing of conspecifics is several thousand times greater than the highest homicide rate in any American city.

The first stable conclusion I reached … was that the only thing brains could do was to approximate the responsivity to meanings that we presuppose in our everyday mentalistic discourse. When mechanical push comes to shove, a brain was always going to do what it was caused to do by current, local, mechanical circumstances, whatever it ought to do, whatever a God's-eye view might reveal about the actual meaning of its current states. But over the long haul, brains could be designed – by evolutionary processes – to do the right thing (from the point of view of meaning) with high reliability. … [B]rains are syntactic engines that can mimic the competence of semantic engines. … The appreciation of meanings – their discrimination and delectation – is central to our vision of consciousness, but this conviction that I, on the inside, deal directly with meanings turns out to be something rather like a benign "user-illusion".