All across the twentieth century, a number of philosophers shifted their attention from the belief that the mind had actually been immaterial and came to think of it as being material and actually being physically connected to the body, given that it is part of it. Armstrong in particular lobbies for people to accept that mental processes should be associated to psychico-chemical statuses present in the nervous system. Exemplifying this through the connection between DNA molecules and living cells, Armstrong demonstrates that mental processes can be likened to DNA molecules, physically influencing the body (Armstrong, 1993, p. 358).
If mental processes are equivalent to physico-chemical processes in the central nervous system, it means that they are also responsible for human behavior. People are generally inclined to believe that there is no connection between the mind and the brain because they cannot understand how a process that is purely physical is capable to determine complex thinking (Armstrong, p. 358).
In general, people who are reluctant to accept materialist theories do so because they have not yet been acquainted with a machine that is capable to produce processes like the ones generated by the mind. However, once they are aware that such mechanisms exist, they are likely to abandon their mentalist convictions and embrace materialist theories, certain that there is nothing more to the mind than purely physical processes (Armstrong, p. 358).