Physicalism assumes that all the facts of our world fit into the physical picture of reality, the notion that the physical theory can offer. Physicalism should not be viewed as a metaphysical concept tied to a particular current physicalism theory. The latter assumes that all the facts of our world can be expressed in the language of the most fundamental scientific theory. If to look at all the diversity of sciences from a reductionist point of view, then it is explained by a hierarchical scheme based on the most fundamental of the sciences – at the moment, this is the physics of the microworld.
Thus, the social sciences, from the physicalist point of view, are reducible to the psychological, the latter, in turn, to neurophysiology. Neurophysiology is reduced to biology, biology – to chemistry, chemistry – to the physics of the macrocosm, the latter – to the physics of the microcosm. “Reduced” here means that the phenomena of one science (reducible) can be described in the language of another science. For example, the facts provided by the social sciences can be described in the language of the psychological and biological sciences; psychological facts can be described in the language of neurophysiological sciences.
In particular, when one smells vanilla, the reductive approach here would be that first, there are signals that the brain gets from the sense organs, which is the field of neurophysiology. Then, the organs of the body interact, which implies the presence of biology. Then, this interaction causes specific chemical reactions that are explained by chemistry. The mentioned reactions are further viewed from the macro- and microcosm’s perspectives.
The possibility of reducing some sciences to others suggests that the facts of one science can be reduced to the points of another, more fundamental science. One of the stumbling blocks for the above scheme is consciousness in its phenomenal aspect since it resists reduction to physical phenomena. Hence, to be in a state of headache means having a certain physiological “problem” in the body, and getting out of this state means correcting this “problem”. The described approach to psychology implies its non-reductiveness, the impossibility of reducing the facts that it describes and explains to more fundamental ones.
However, it might be said that the presented above issue is not as crucial as one regarding the core ideas of idealism. The latter – most of its doctrines – assumes that reality is defined by human consciousness. Such a substantial impact of the subjective element reduces the importance of objective truths that are determined by the laws of nature. The reality is not real if it is considered out of the human mind.