Consciousness
I guess all Descartes knew for certain was that HE existed. In scientific sense, you can't be privy to anyone else's mind. Their own sense of self is only available to you through your senses (as is everything that isn't your self). So you have to take on faith, as in educated deduction, that other people have minds or souls or whatever. Until recently (last couple of hundred years), at least in "Western" thought, animals were thought to be merely patterns, algorithms. The vivisection of creatures for medical research (which continues today by the way) was easily explained away by the notion that since they had no souls, they couldn't really feel anything either (Harari: Homo Deus). They were like moving plants that had automatic responses, as might a robot. The idea is alive and well, judging by my many arguments with people who think that shellfish couldn't possibly feel pain without a central nervous system like ours. Why is there a cut-off point betwee...