A layman, confronted with "abstract" art, is apt to lapse into the language of the Two Black Crows and say: "What causes that?" Probably two things: 1) the development of photography, which reproduces reality much better than 'any painter could; 2) the progress of experimental science.
About 1870, artists began retreating from realism. With every fresh retreat they dug themselves a new redoubt, hoisted a flag and proclaimed a new ism. Impressionism and neoImpressionism held that artists should paint with prismatic colors, imitating the effect of light. Synthetism held that they should not....