Abstract painting in the case of Mondrian or Malevich was thought of as a distillation of visual reality.
The term ‘concrete’ referred to painting that was autonomous, that referred to nothing outside itself from objective reality.
Kupka
“Great art is to create from the invisible and intangible purely and simply experienced, a visible and tangible reality; a reality that is not simply a copy or image, but which, as the created work, has a soul and life of its own, which imposes itself supremely on the senses of the spectator.”