Already the philosophers had expressed interest in the soul, but until the 19th century the psychology did not achieve to become an empirical science. In 1879, Wilhelm Wundt installed the first laboratory of psychology in Leipzig, fact that can be considered as the birth of the experimental psychology.
According to Wundt, the main mission of the psychology is the decomposition of the sensations into simple elements, for being able to go to the depth of the problem.
In opposition to Wundt psychological atomism came in 1920, the Gestalt psychology, or psychology of the form. That theory sustains that all psychic phenomena constitute one set of different nature compared with the simple sum of the elements that compose it.
The behaviourism (psychology of the behaviour), created by James B. Watson, considers that the psychology must only study the external behaviour. It is based, among other topics, in the famous experiences with dogs that the Russian physiologist Ivan Pavlov made. He observed that when the bell rings, moments before giving food to the dogs, these segregated saliva by the simple fact of hearing the bell ringing. It had been created one conditioned reflex. Watson provoked one sensation of fear in certain children with the presence of soft and hairy objects, producing repeatedly one strong and unpleasant sound while showing to them a rabbit. The behaviourism explains that all the complicated behaviours are conditioned reflexes. Watson considers that the education must consist in the creation of some pre-selected reflexes.
The north-American psychologist B. F. Skinner is one predecessor of the modern behaviourism, which brought big contributions to the psychology of learning. With the own instrument for experiences, the “box of Skinner”, he achieved that one she-rat can learn to obtain food pressing one hand spike. The ethology, which has as its subject the study of the behaviours and habits of animals’ life, can help the understanding of the behaviour of men. In that sense, the researches of Konrad Lorenz are very interesting (Birds Behaviour).
One the most remarkable persons inside the evolutionary psychology is Jean Piaget that, already in the 1920´s, studied the psychic evolution of the children, specially the formation of the intelligence.
Sigmund Freud was the founder of the psychoanalysis and he had a strong influence in the infantile psychology. Freud accentuated the main importance that the first years of life have in the formation of the personality. According to Freud, the conflicts that had been repressed during the infancy conduct to some posterior psychic perturbations, when the adult age arrives. Freud considered that one of the main causes of those unconscious conflicts is the libido: the impulse for the sexual pleasure.
After a certain while, his students Adler and Jung separated from him, because they disagreed of some aspects of his theories about sexuality. The neo-Freudianism, which appeared around the 1940´s, revised the theory of Freud, converting the psychoanalysis into a social explanatory psychology of the relations between the individual and the society.
Nowadays, the differences between the different schools have been reduced and the psychology is divided into several specialised branches.