While a student at the latter, he focused on the link between physics and psychology, in the course of which he studied with two leading scholars in those fields, Max Planck and Carl Stumpf, respectively.

In 1910–13, he was an assistant at the Psychological Institute in Frankfurt, where he worked with fellow psychologists Max Wertheimer and Kurt Koffka.

He and Koffka functioned as subjects for Wertheimer's now-famous studies of apparent movement (or the phi phenomenon), which led them in turn to conclusions about the inherent nature of vision.

They collaborated on the founding of a new holistic attitude toward psychology called Gestalt theory (from the German word for "shape" or "form"), aspects of which are indebted to the earlier work of Stumpf (Köhler's teacher) and Christian von Ehrenfels (whose lectures at the University of Prague Wertheimer had attended).

In an introduction to the book, The Task of Gestalt Psychology, Carroll Pratt emphasizes Köhler's irritation at misinterpretation of his famous quote, "The whole is different from the sum of its parts".

Though perhaps a simple error made in translation, many lectures in textbooks of modern-day psychology refer to Gestalt theory by saying "the whole is greater than the sum of its parts".

Köhler concluded that the chimps had not arrived at these methods through trial-and-error (which American psychologist Edward Thorndike had claimed to be the basis of all animal learning, through his law of effect), but rather that they had an insight, in which, having realized the answer, they proceeded to carry it out in a way that was, in Köhler's words, "unwaveringly purposeful."

The conclusions drawn from the experiments with apes were that these animals exhibit insight and that they demonstrate intelligent behaviour that is common in humans.

[2] Köhler points out that a downfall of educational psychology at the time of the experiments with apes was that it had yet to create a test that was capable of assessing how far mentally healthy and mentally-ill children could go in particular situations.

Köhler believed that studies of this type could be performed on young children, and that future research should focus on these possibilities.

He stated that: "where the lack of human standards makes itself so much felt, I should like to emphasize particularly the importance and- if the anthropoids do not deceive us- the fruitfulness of further work in this direction".

If one person was tested for sensations regarding the colour red, these descriptions were simply shared among followers of the discipline.

[citation needed] Köhler was also vocal in his stance against behaviorism, another competing school of thought in North America.

Inner thoughts, feelings, and processes that occurred between the presentation of a stimulus and the onset of behaviour were considered part of a black box not easily understood.

He argued that the behaviourists focused solely on overt behaviours in order to make inferences concerning human functioning.

Using his background in physiology, Köhler suggested that covert behaviours (such as heart rate and blood pressure) could offer additional insight into how we function and interact with the environment.

In Gestalt Psychology, Köhler describes advancements made in physiological research and the tools created to measure covert behaviours.

Covert behaviours such as increased heart rate could provide additional insight into how people interact with particular stimuli.

Drawing upon his personal experience and interest in the field of physics, Köhler posed the example of two physicists observing a galvanometer (an instrument that detects and measures electric current) and making inferences based on the information it provides.

Köhler also had many well-known assistants at the institute, including Karl Duncker, whose work revolved around problem solving and induced movement.

The regime started practicing discriminatory policies against Jews, and dismissed any professors with a Jewish background from German universities.

Max Planck, the well-known physicist, petitioned Hitler to stop the dismissal of Jewish professors, stressing their importance regarding scientific contributions.

It was written for the Deutsche Allgemeine Zeitung and is officially the last published article that openly attacked the Nazi Regime during their reign.

Although Köhler did not interfere, he later contacted the institute rector, Eugen Fischer, complaining that an unannounced raid had occurred.

[4] This drew the attention of the Ministry and they would finally intervene in July 1934 by running an investigation of the interactions between Köhler and the rector as well as the personal attacks he received from the German student organizations.