matter because in psychology, everything is matter–what we say, don’t say, think, don’t think, feel, don’t feel, do, don’t do, see, don’t see–it is all matter for examination, observation, and understanding. 

matter because grey matter–a type of brain tissue.  It is within the human brain where most psychological work takes place. Even if we integrate physical movement and techniques, the brain is still intimately involved.  

The grey matter is the seat of a human’s unique ability to think and reason. The grey matter is the place where the processing of sensation, perception, voluntary movement, learning, speech and cognition takes place….Grey matter throughout your central nervous system is essential for controlling movement, memory and emotions.