[What can qualia be? The monistic views]

Phenomenal properties, also named qualia (that is, the qualities of human experiences, e.g. the senses of red, of salt, of pain, qua senses) create a hard problem for philosophy. It is claimed that phenomenal properties are radically different to the physical ones: they are intrinsic (their essence is totally confined within the limits of their existence), they depend on mind, they are accessible only privately, by introspection and they are infallible, in the sense that the experience of a quale is identical to its existence. On the contrary, physical properties are dispositional (their essence is defined through their causal consequences), they exist independently of mind, they are accessible to public observation and are liable to verification or falsification. The faculty of philosophy, named philosophy of mind, is systematically interested in qualia. In the present paper some of the main monistic philosophical approaches to qualia are discussed. The main common characteristic of monistic views is that (contrary to dualistic views) they purport that: two radically different substances cannot exist, side by side, within the same world (our world). Thus, there are either physical properties, or phenomenal properties, but not both. The monistic theories, supporting that in our world there are only physical properties, or properties totally reducible into physical ones, are named physicalism (or according to a more traditional nomination, materialism). On the other hand, monistic theories maintaining that all existing properties are phenomenal, or properties reducible into phenomenal ones, are named phenomenalism. The main arguments for physicalism are: (a) the scientific principle of the causal closure of the universe (every event has one physical cause), (b) the dependence of every well-studied mental phenomenon, from a physical phenomenal, such as the function of the neural system. Dualists counterattack physicalism with mental experiments (such as, the experiments concerning philosophical zombies) in order to demonstrate that qualia are irreducible entities. The main physicalistic options are eliminativism, the theories of identity, functionalism and representationalism. The main argument for phenomenalism is that physical properties and physical knowledge of them, as well, are reducible into and derived from experiences. On the other hand, opponents of phenomenalism retort that our world comprises spatiotemporal parts inaccessible to experience (f.e. the microworld of atomic physics, the world before the appearance of intelligent beings). Yet, some phenomenalists claim that phenomenal properties can be either real (experienced) or potentially real (what one would experience if one could observe this or that spatiotemporal part of the world). According to a third, agnosticistic opinion, named mysterianism, the human mind lacks the capacity of bridging the explanatory gap between physical and phenomenal identities. Many opponents of this theory claim the historically proved ability of human mind to find solutions for difficult problems of our world through scientific knowledge and based on it natural philosophy.