Applied History of Psychology/Philosophical Roots of Psychology
Socrates, Plato and Aristotle 
From approximately 600 to 300 BC, Greek philosophers conjectured on a wide range of topics relating to what we now consider psychology. For example, Socrates and his followers, Plato and Aristotlewrote about pleasure, pain, knowledge, motivation, rationality, among other topics. They theorized about such things as whether human traits are innate or the product of experience, which continues to be a topic of debate even today. They also considered the origins of mental illness, with both Socrates and Plato focusing on psychological forces as the root of the such illnesses.
Descartes and mind-body dualism 
René Descartes was a French mathematician and philosopher from the 1600's. He theorized that the body and mind are separate entities. The body was viewed as a physical entity and the mind as a spiritual entity. Descartes believed that the two interacted only through a tiny structure at the base of the brain called the pineal gland. His position of the mind and body as separate entities became known as dualism. According to dualism, the body's behavior is scientifically measureable, however the mind is not, as it transcends the material world.
Hobbes and Locke's monism 
Thomas Hobbes and John Locke were English philosophers who disagreed with the concept of dualism. They argued that all human experiences are physical processes occurring within the brain and nervous system. Thus, their argument was that sensations, images, thoughts and feelings are all valid subjects of study. As this view holds that the mind and body are one and the same, it later became known as monism. Today, most psychologists reject a rigid dualist position since many years of research has indicated that the physical and mental aspects of human experience are intertwined. The fields of psychoneuroimmunology and behavioral medicine explicitly focus on this interconnection.