The theory of materialism holds that the only thing that exists is matter or energy; that all things are composed of material and all phenomena (including consciousness) are the result of material interactions. In other words, matter is the only substance, and reality is identical with the actually occurring states of energy and matter.
The obvious question that arises with materialism is what about non-material elements of the world like consciousness? There are several different attempts to deal with this such as eliminative materialism which holds conscientiousness is an illusion and mental phenomena simply do not exist at all. Another position is reductive materialism that claims that all psychological states of the mind can be reduced to physical states in the brain (or sometimes more broadly, in the body). This view allows for mental states, they are however explicable in purely physical terms by observing the bodily states.
EVIDENCE FOR MATERIALISM
The evidence for materialism is that nearly any aspect of the mind -- temperament, memories, appetite, and so on -- can be disrupted by damage to specific areas of the brain and modern brain imaging techniques can even detect brain activity correlated with thought and that brain activity in the prefrontal and parietal cortex may precede conscious decision-making by as much as ten seconds before a decision is consciously made. However, as it is often pointed out just because the mind is affected by the brain, and its states are affected by the brain’s functioning it doesn't follow that the world is composed only of material substance. In fact, all that follows is that there is a close connection between the mind and the brain in this life.
As the philosopher Tom Morris put it  :“It is true that mental function seems to depend on the chemical state of the brain. But consider this analogy. If my car runs out of gas on the interstate, it will stop. So will I. But I am not the same thing as my car. I am not even made of the same stuff as my car. Yet I am affected by its various physical states, and by its proper functioning. When it goes fast, I am going fast; when it sits in traffic, I sit in traffic. When it has a problem, I have a problem. Yet I am obviously a different entity from it.” The argument that brain states prove materialism is therefore inconclusive. Furthermore, there are other theories such as panpsychism where a brain/mind connection follows and yet are free from many of the problems associated with materialism.
Rationality is impossible with materialism
One criticism of the materialistic solution is the claim that rationality is impossible because mental events are nothing but a series of physical events in the brain. This would mean that the theory of materialism itself is nothing but brain events and any rival theory is likewise a different series of events. In that case, how can one set of motions in the brain said to constitute truth, whereas others would constitute a falsehood? If any metaphysical theory is just a physical occurrence in somebodies head, why should one of those occurrences be taken seriously, and the others discounted as wrong?
As the philosopher John Polkinghorne put it :"The reductionist program ... destroys rationality. Thought is replaced by electro-chemical neural events. Two such events cannot confront each other in rational discourse. They are neither right nor wrong. They simply happen … The very assertions of the reductionist himself are nothing but blips in the neural network of his brain. The world of rational discourse dissolves into the absurd chatter of firing synapses. Quite frankly, that cannot be right and none of us believes it to be so."
Materialism doesn’t take our thoughts seriously
Materialism doesn't take our thoughts seriously, but we certainly do. It claims that our thoughts are the results of activity in the brain, but this does not do justice to our mental life because we do take our thoughts very seriously indeed. We are bothered by them, brood about them, and we seem to take actions based on them. If they are nothing but the a vague byproduct of material events which occur in our brains, bearing no actual relation to them, it is strange that they should play such an important part in our lives. It fact, it could be claimed that our thoughts and feelings are the things we hold most near and dear. Materialism therefore denies the most intimate and real thing that we know - our concious existence!
Materialism denies free will
It has also been argued that materialism denies free will. It necessarily comes from the fact that physical matter and energy are inevitably subjected to physical 'laws' and conditions and everything that you think or do follows from the laws of nature. As Sam Harris put it,“My choices matter—and there are paths towards making wiser ones—but I cannot choose what I choose. And if it ever appears that I do—for instance, after going back between two options—I do not choose to choose what I choose. There is a regress here that always ends in darkness.”
Physics denies materialism
Although it has not been conclusively proved some modern day physicists such as Paul Davies and John Gribbin have argued that scientific finds in physics such as quantum mechanics and chaos theory have disproven materialism. Paul Davis said :
“... Quantum theory … totally transformed our image of matter. The old assumption that the microscopic world of atoms was simply a scaled-down version of the everyday world had to be abandoned. Newton's deterministic machine was replaced by a shadowy and paradoxical conjunction of waves and particles, governed by the laws of chance, rather than the rigid rules of causality. An extension of the quantum theory goes beyond even this; it paints a picture in which solid matter dissolves away, to be replaced by weird excitations and vibrations of invisible field energy. Quantum physics undermines materialism because it reveals that matter has far less 'substance' than we might believe. But another development goes even further by demolishing Newton's image of matter as inert lumps. This development is the theory of chaos, which has recently gained widespread attention.”
Davies's and Gribbin's objections are shared by proponents of digital physics who view information rather than matter to be fundamental, and were also shared by founders of quantum theory such as Max Planck who wrote :
“As a man who has devoted his whole life to the most clear headed science, to the study of matter, I can tell you as a result of my research about atoms this much: There is no matter as such. All matter originates and exists only by virtue of a force which brings the particle of an atom to vibration and holds this most minute solar system of the atom together. We must assume behind this force the existence of a conscious and intelligent Mind. This Mind is the matrix of all matter.”
Philosophers such as Alfred North Whitehead have drawn on the indeterminacy observed by Quantum physics to defend panpsychism. They see quantum indeterminacy and informational but non-causal relations between quantum elements as the key to explaining consciousness  . Recent work on this approach has also been undertaken by William Lycan (1996) and Michael Lockwood (1991).
Evolution, non-emergence and materialism
The most popular empirically based argument for panpsychism stems from Darwinism and is a form of the non-emergence argument. This argument begins with the assumption that evolution is a process that creates complex systems out of pre-existing properties but yet cannot make “entirely novel” properties  . William Kingdon Clifford argued that:
“… we cannot suppose that so enormous a jump from one creature to another should have occurred at any point in the process of evolution as the introduction of a fact entirely different and absolutely separate from the physical fact. It is impossible for anybody to point out the particular place in the line of descent where that event can be supposed to have taken place. The only thing that we can come to, if we accept the doctrine of evolution at all, is that even in the very lowest organism, even in the Amoeba which swims about in our own blood, there is something or other, inconceivably simple to us, which is of the same nature with our own consciousness"
One major problem with materialism is found with the theory of how consciousness emerges from matter and many people have argued that emergentism and thus materialism is inconsistent. The arguments begins by asserting that a proton, say, is not conscious, but that a system (eg, myself with 5 x 10^28 protons) can be. This seems very implausible because the number would be a remarkable new constant of nature. Presumably it would have to be very large, otherwise we would certainly be in the situation where everything, except very tiny microscopic systems are conscious, which would essentially be equivalent to panpsychism. Then it appears hard to see how consciousness could exist for some number, N, of nucleons, but not for N-1. We would not expect such a fundamental difference come from such a small change of nucleons.suddenly’ this process would cease and that all states would become equally happy, which would imply that consciousness had dropped to zero.
In the words of David Griffin : “The difference between the proton and the psyche is one of degree and not of type (in an ontological sense). One who holds otherwise is a dualist, however an odious description it may be.” The argument that consciousness can not emerge from matter can be traced back to the Ancient Greek philosopher Parmenides, who argued that ‘ex nihilo nihil fit’ - nothing comes from nothing and thus the mental cannot arise from the non-mental.
As Thomas Nagel's argued : “there are no truly emergent properties of complex systems. All properties of complex systems that are not relations between it and something else derive from the properties of its constituents and their effects on each other when so combined.” In fact there are a number of popular arguments against materialism start from a premise about an epistemic gap between physical truths about truths about consciousness, and infer an ontological gap between physical processes and consciousness.
Arguments of this sort include the conceivability argument, the knowledge argument, the explanatory-gap argument, and the property dualism argument. Of course materialists reply that epistemic premises do not entail ontological conclusion. Nevertheless, before materialists can conclude that their case is won they must solve the problem of emergentism since positions like panpsychism have all the benefits but none of the problems of explaining emergentism.
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