The saying "never too much of a good thing" may not always be true – a word about the processing of information by humans
When comparing pairs, we are able to see very slight differences: in shape, intensity (of timbre and sound), quality (figure size, sound pitch) etc. However, if using this possibility, we started making sequences (motifs, pictures, decoration strings along a house wall) with elements which only slightly differ from one another, we would not be able to understand their arrangement, we wouldn’t see their sequence structure, we wouldn’t attach any significance to it. Such a signal would exceed our ability to receive and process signals and it wouldn’t differ from the information noise around us.
In order for a signal to be distinguishable from the noise, to be received and understood as intended by its sender, it must be made of a small number of elements which differ significantly, and what is more, these elements must repeat in a given message time and again as well as it must be possible to combine them in larger units (bunches, packages, motifs).
We treat sounds which make music in a similar way. We categorize slight differences in their pitch, particularly differences between two sounds which differ with regard to their pitch . Categories which correspond to the levels of the European scale are so broad that even when we hear songs sung by individuals who, in our opinion, do not sing in tune, we are able to recognize Happy birthday, the national anthem and several Christmas carols.
Psychological research summarized in the frequently quoted article by George A. Miller from 1956  showed that a human who has to evaluate and classify a given phenomenon without any reference to external models, uses scales which do not exceed seven, plus or minus two, categories (humans have considerable problems identifying different odours, but we do better when it comes to perceiving colour differences). The number of colours that humans are able to distinguish in a rainbow does not exceed six or seven. Similarly, the capacity of our short-term memory does not exceed a similar number of entries (if we want to do bigger shopping, we prefer to make a shopping list). Can it thus be stated that seven notes making up the European musical scale constitute a natural adaptation of an acoustic material to tasks which humans set when they create cultural codes?
 Rakowski, Andrzej: Kategorialna percepcja wysokości dźwięku w muzyce, Warsaw 1978, AMFC.
 Miller, George A: The magical number seven plus or minus two. Psychological Review, 63, (1956) pp. 81-97.
Additionally, we recommend the following entry in the English version of Wikipedia: The Magical Number Seven, Plus or Minus Two: Some Limits on Our Capacity for Processing Information, shortly describing the article by George A. Miller.
Kacper Miklaszewski (born in 1949) – was awarded an MA in Piano at the Rimski-Korsakov Conservatory in Leningrad (Saint Petersburg) (1974), he also studied at the Music School, University of Illinois at Urbana-Champaign. In 1984, he got a PhD in the theory of music at the Chopin Academy of Music (currently Fryderyk Chopin University of Music) in Warsaw. In 2000-2010 he lectured on the basics of the psychology of music and he conducted a seminar on music criticism at the Institute of Musicology of the University of Warsaw. He is a musical journalist working inter alia for a music journal “Ruch Muzyczny” and for Program II Polskiego Radia (Polish radio channel).