Psychology

Psychology is an field of study of the connection of behavior, perception and cognitive process. It’s branches are neuropsychology, linguistics, sociology and cognitive psychology.

Etymology
1650s, "study of the soul," from Modern Latin psychologia, probably coined mid-16c. in Germany by Melanchthon from Latinized form of Greek psykhē "breath, spirit, soul" (see psyche) + logia "study of" (see -logy). Meaning "study of the mind" first recorded 1748, from Christian Wolff's "Psychologia empirica" (1732); main modern behavioral sense is from early 1890s.

Early psychological thoughts
Many cultures throughout history have speculated on the nature of the mind, heart, soul, spirit, brain, etc. For instance, in Ancient Egypt, the Edwin Smith Papyrus contains an early description of the brain, and some speculations on its functions (described in a medical/surgical context). Though other medical documents of ancient times were full of incantations and applications meant to turn away disease-causing demons and other superstition, the Edwin Smith Papyrus gives remedies to almost 50 conditions and only two contain incantations to ward off evil.

Sigmund Freud
Freud states explicitly that his concept of the unconscious as he first formulated it was based on the theory of repression. He postulated a cycle in which ideas are repressed, but remain in the mind, removed from consciousness yet operative, then reappear in consciousness under certain circumstances. The postulate was based upon the investigation of cases of hysteria, which revealed instances of behaviour in patients that could not be explained without reference to ideas or thoughts of which they had no awareness and which analysis revealed were linked to the (real or imagined) repressed sexual scenarios of childhood. In his later re-formulations of the concept of repression in his 1915 paper 'Repression' (Standard Edition XIV) Freud introduced the distinction in the unconscious between primary repression linked to the universal taboo on incest ('innately present originally') and repression ('after expulsion') that was a product of an individual's life history ('acquired in the course of the ego's development') in which something that was at one point conscious is rejected or eliminated from consciousness.

Fields
Neuropsychology

Social psychology

Linguistics

Cognitive psychology