The term Gestalt appears for the first time in Gestalt psychology, created by Wertheimer, Keller, Koffka and Rubin, to mark an entity, good form. Elements do not determine an entity, and an entity is not a mere set of elements. It should be specified that a particular part of an entity is not the same when alone or included in some other entity because that part absorbs the characteristics coming from its place and function in various entities (for example, a scream in an empty street is not the same as a scream made by children playing). The proof for gestalt therapy's success is an introspective report on subjective perception of a person's improvement, or more precisely "maintenance and development of balance and good condition of the whole organism." To scientifically approach gestalt psychotherapy, it is necessary to operationalize positive effects or changes that this therapy brings. All terms used to validate the effects of psychotherapy are subjective constructs. An introspective perception of improvement is an indicator of a positive effect of psychotherapy. Intersubjective consent, that clients give in psychotherapy, after some time of applying gestalt therapeutic techniques results in improvement, is a guarantee that the achieved therapeutic effect is objective. Gestalt psychotherapy is a branch of psychotherapy that bases its theory on a so called "empty chair". This psychotherapeutic school's basic goals are solving the problem of the now and here, and as the other psychotherapeutic schools, it bases usually its research methods on a case study. This is clearly seen in journals and articles which discuss this psychotherapeutic school. As a therapy, it is suitable for treating mild mental disabilities and anxiety. Its therapists are constantly improving themselves and students, or psychotherapists to be, consider it to be challenging.