Dualism
The theory of dualism in terms of mind and matter was first theorised by Rene Descartes and was called as Cartesian Dualism. According to him, mind was divided into two parts: res extensa (extended substance) and res cogitans (thinking substance). Res extensa is the physical substance, which is extended in space; whereas, res cogitans is that which has no physical body and attributes to the thought process of a person. According to Descartes, it was this non-physical part of you which forms the real you. Further, it is the two-way interaction between the physical body and non-spatial thinking substance which ensures that the body is your body and no one else'. However, this theory failed to explain the way the thinking substance affected the physical body and its movements and hence, this theory was discarded. Thus came into being another theory -- Popular Dualism. According to this theory, human beings were just ghost in a machine, where the machine was a human body and ghost was a spiritual substance. However, even though this theory was able to explain the interdependence and freedom of the two forms of the mind, it fails to explain or provide proof of the fact that the spiritual form lives even after the physical form dies. In order to explain this pitfall, therefore, another theory was formed. This theory was called as the Property Dualism. According to this theory, the mind was a physical matter and the thought processes were determined by the physical properties of this mind, which only appeared after the mind had organised its physical matter into a highly organised form. This theory had several other bifurcations, one amongst them being elemental-property dualism, which explained that this physical matter that had properties was in the form of electro-magnetic pulses. However, this theory claimed that these properties were irreducible and this formed a contradiction to its own claims. Thus, several other arguments came into being such as arguments of religion, argument of irreducibility and argument from introspection. However, all theories of dualism have one problem -- they are yet to prove the final form that is simply irreducible.
Materialism
According to the Identical Materialism or Reductive Materialism, the different mental states are identical to the physical states of the brain. The theory believes that since the scientists are still working on brain research, a few hidden states of the brain are yet to reveal themselves and therefore, certain phenomenon with respect to the brain are yet to be explained. The materialism theorists give four reasons for their belief in this theory: firstly, the human body is formed of a complex organised cellular structure, which begins its journey from a fertilised egg to a complete human body based on the information coded in its DNA. Thus, it is a purely physical process involving neurosciences with no scope of any outside forces being involved. Secondly, the concept of behaviour controlling capacities of the brain can only be explained by using this theory of evolution. This theory explains that our behaviours are a result of neural activity in the brain. Thirdly, it has been proved by science that all mental phenomena depend on the neural behaviour of the brain. Lastly, the neurosciences are evolving by the day and just as the genetics have been able to break the cell structure down to nuclei, there is no reason to believe that further breakdown is not possible. Some of the other theories offer arguments against the materialism theory. For instance, the theory of introspection believes that once you start introspecting, certain aspects are revealed which, in no way, are relating to the physical state of the mind. However, this theory does not stand for long against the materialism theory for not all states can be felt. For instance, science has proved that rise and fall in temperature is owing to an increase or decrease in the movement of cells. However, we do not feel this kinetic movement of cells and thus, theory of introspection cannot claim to falsify the theory of materialism. Further, one cannot feel everything in order to prove that that thing exists. For instance, we know that a bat has ectoplasmic activity; however, we can never understand how that feels for the bat. Second objection against materialism theory is that one cannot indentify mental states with brain states for one cannot limit one's beliefs to certain part of the brain. To this, the theory of materialism retorts by saying that it is understood and a known fact that the brain functions in different modes or media and therefore, it is possible for the brain to feel certain sensations and feelings which are yet to be identified in physicality, but are within the reach of physical sciences.
