act-object psychology also called act-contentobject psychology, a philosophical theory that identifies in every psychological state a mental act, a lived-through phenomenological content, such as a mental image or description of properties, and an intended object that the mental act is about or toward which it is directed by virtue of its content. The distinction between the act, content, and object of thought originated with Alois Höfler’s Logik (1890), written in collaboration with Meinong. But the theory is historically most often associated with its development in Kazimierz Twardowski’s Zur Lehre vom Inhalt und Gegenstand der Vorstellung (‘On the Content and Object of Presentations,’ 1894), despite Twardowski’s acknowledgment of his debt to Höfler.
Act-object psychology arose as a reaction to Franz Brentano’s immanent intentionality thesis in his influential Psychologie vom empirischen Standpunkt (‘Psychology from an Empirical Standpoint,’ 1874), in which Brentano maintains that intentionality is ‘the mark of the mental,’ by contrast with purely physical phenomena. Brentano requires that intended objects belong immanently to the mental acts that intend them – a philosophical commitment that laid Brentano open to charges of epistemological idealism and psychologism. Yet Brentano’s followers, who accepted the intentionality of thought but resisted what they came to see as its detachable idealism and psychologism, responded by distinguishing the act-immanent phenomenological content of a psychological state from its act-transcendent intended object, arguing that Brentano had wrongly and unnecessarily conflated mental content with the external objects of thought.
Twardowski goes so far as to claim that content and object can never be identical, an exclusion in turn that is vigorously challenged by Husserl in his Logische Untersuchungen (‘Logical Investigations,’ 1913, 1922), and by others in the phenomenological tradition who acknowledge the possibility that a self-reflexive thought can sometimes be about its own content as intended object, in which content and object are indistinguishable. Act-object psychology continues to be of interest to contemporary philosophy because of its relation to ongoing projects in phenomenology, and as a result of a resurgence of study of the concept of intentionality and qualia in philosophy of mind, cognitive psychology, and Gegenstandstheorie, or existent and non-existent intended object theory, in philosophical logic and semantics. See also BRENTANO, HUSSERL, INTENTION — ALITY, MEINONG , PHILOSOPHY OF MIND , POL — ISH LOGIC , QUALI. D.J.