Activity theory
Activity theory (AT; ) is an umbrella term for a line of eclectic social sciences theories and research with its roots in the Soviet psychological activity theory pioneered by Lev Vygotsky , Alexei Leont'ev and Sergei Rubinstein. These scholars sought to understand human activities as systemic and socially situated phenomena and to go beyond paradigms of reflexology (the teaching of Vladimir Bekhterev and his followers) and classical conditioning (the teaching of Ivan Pavlov and his school), psychoanalysis and behaviorism. It became one of the major psychological approaches in the former USSR, being widely used in both theoretical and applied psychology, and in education, professional training, ergonomics, social psychology and work psychology.
Intentionality
The concept of intentionality was reintroduced in 19th-century contemporary philosophy by Franz Brentano (a German philosopher and psychologist who is generally regarded as the founder of act psychology, also called intentionalism) in his work "Psychology from an Empirical Standpoint" (1874). Brentano described intentionality as a characteristic of all acts of consciousness that are thus "psychical" or "mental" phenomena, by which they may be set apart from "physical" or "natural" phenomena.
Brentano coined the expression "intentional inexistence" to indicate the peculiar ontological status of the contents of mental phenomena. According to some interpreters the "in-" of "in-existence" is to be read as locative, i.e. as indicating that "an intended object ... exists in or has "in-existence", existing not externally but in the psychological state" (Jacquette 2004, p. 102), while others are more cautious, stating: "It is not clear whether in 1874 this ... was intended to carry any ontological commitment" (Chrudzimski and Smith 2004, p. 205).