"Whoever wants to portray something that does not exist has to obey certain rules. Those rules are more or less the same as for the teller of fairy tales: he has to apply the function of contrasts; he has to cause a shock.… That is why such a game can be played and understood only by those who are prepared to penetrate the surface, those who agree to use their brains, just as in the solving of a riddle. It is thus not a matter for the senses, but rather a cerebral matter. Profundity is not at all necessary, but a kind of humour and self-mockery is a must."
(Escher, in Escher, 1989, p. 136)

Interestingly enough, Escher’s name is mentioned more often in introductory mathematics and psychology texts than in introductions to art history. The fact is that Escher did not consider aesthetic value as an end in itself, but rather as the outcome of meticulous cutting or engraving of wood and a rigorous application of his far-reaching studies in geometry and perception.

Mathematics and geometry teachers often use his prints to demonstrate to their students how science can be a source of poetry and beauty. Psychology textbooks present them as proof of the claim that our perceptions of reality are in fact “constructions.” Thus, three traditionally unrelated disciplines intersect in Escher’s work.