Physicalism (materialism)
"This is the view that there's only physical stuff in the world. It says that there's no immaterial substance in the world. Physicalism [ˈfɪzɪkəlɪz(ə)m] states that minds and bodies are made of exactly the same thing."
Three different ways of expressing the view that is physicalism
Identity [aɪˈdɛntɪti] theory
Functionalism [ˈfʌŋkʃənlɪz(ə)m]
Logical behaviorism
Identity theory
"It says that a thought is identical with a particular physical state of the body and brain. Identity theory says that for every psychological state that a human being is in, there is a corresponding physical state."
Identity theory as a reductionist view
"It's reducing the psychological thoughts that we have to the physical. It's saying that if we think very carefully, the thought that I'm going to go to Paris next week, can be re-described in purely physical terms. It can be re-described in terms of a mix of chemistry [ˈkɛmɪstri] and hormones [ˈhɔːməʊnz] and atomic structures, that are going on in my body right now."
Putnam’s thought experiment [ɪksˈpɛrɪmənt] about an octopus[ˈɒktəpəs]
"In 1967 in his paper Hilary Putnam wrote about problems with identity theory. He offered to think about an octopus. Octopuses [ˈɒktəpəsɪz] are very different from humans. Their brains are probably made up of slightly different chemicals to human brains. And yet, we don't want to say that octopuses can't feel pain. It is a problem for identity theory because this theory is saying that each type of psychological state can be reduced to a particular brain state. So we're saying that pain is just the stimulation of C-fibre [siːˈfaɪbə], but that can't be right, because we want to say that octopuses can feel pain. But octopuses don't have the same sort of C-fibre as human beings.
We're saying that pain and other psychological states are identical with particular states of the body. But the states of the body that they're identical with could vary from species [ˈspiːʃiːz] to species. And possibly, more frighteningly, could even vary across human to human. Well, this greatly reduces the strength of the identity theory."
The issue of multiple realisability
"What Putnam was saying is that a particular psychological state, like pain, can have different physical realisers, can be made of different physical stuff dependent on whether you're a human, whether you're an octopus or whether you're an alien [ˈeɪljən]. We want to say that humans, octopuses and these aliens can still all feel pains, even though the stuff that makes up those pains, the stuff that the identity theorist says the pain is identical with, is completely different."
Functionalism
"When you're thinking about psychological states, we should think about what they do and not what they're made of."
SOURCES
'Introduction to Philosophy' course (the University of Edinburgh)
https://www.coursera.org/learn/philosophy