Karl Duncker

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Karl Duncker (2 February 1903, in Leipzig – 23 February 1940) was a Gestalt psychologist. He attended Friedrich-Wilhelms-University from 1923 to 1923, and spent 1925–1926 at Clark University in Worcester, MA as a visiting professor, where he received a masters in arts degree.[1] Until 1935 he was a student and assistant of the founders of Gestalt psychology in Berlin: Max Wertheimer, Wolfgang Köhler and Kurt Koffka. In 1935, exiled by the Nazis, he got an assistantship in Cambridge with Frederic Charles Bartlett and later immigrated to the US, where he was again an assistant of Wolfgang Köhler’s at Swarthmore College. He committed suicide in 1940 at 37 years of age. He had been suffering from depression for some time and had received professional treatment.

His younger brother Wolfgang Duncker, a communist in exile in Moscow, was arrested in 1938 during the Great Purges and died in the Gulag. Their parents were the well-known socialist and later communist propagandists Hermann and Käte Duncker.


Duncker coined the term functional fixedness for describing the difficulties in visual perception and in problem solving that arise from the fact that one element of a whole situation already has a (fixed) function which has to be changed for making the correct perception or for finding the solution to the problem.[2]

The candle problem (Karl Duncker, 1945).

In his "candle problem" the situation was defined by the objects: a candle, a box of thumb-tacks and a book of matches. The task was to fix the candles on the wall without any additional elements. The difficulty of this problem arises from the functional fixedness of the box, which originally contained thumb-tacks. It is a container in the problem situation but must be used as a shelf in the solution situation.

Other examples for this type of mental restructuring are:

  • an electromagnet must be used as part of a pendulum
  • a branch of a tree must be used as a tool
  • a brick must be used a paper weight
  • another meaning of a word must be found that is different from the meaning within the context of the sentence



  1. ^ Schnall S. 2007. Life as the Problem: Karl Duncker's Context. In Thinking in Psychological Science: Ideas and Their Makers, editor: Jaan Valsiner. Transaction.
  2. ^ Zur Psychologie des produktiven Denkens, Springer, Berlin 1935