Questions of the objects of knowledge and types of realism

The problem of the existence of the objects of knowledge is the main problem in the controversy between realism and anti‐realism. This controversy appears on three levels: (i) perceptions, (ii) concepts, (iii) scientific theories. According to perception‐realism, things exist objectively; according to subjective idealism, they are only bundles of impressions. According to conceptual realism, genera (classes) exist objectively; according to nominalism, they do not exist (there are only general names). According to scientific realism, the objects of confirmed theories, including unobservable entities, exist objectively; according to phenomenalism, only observable bodies exist. On each level a naive realism and a critical realism is distinguished. On the level of scientific theories direct objects (ideal models) are distinguished from ultimate objects (real entities).