Impressionism is a divergence from both positivism (i.e. Reality as in the object in the external world) and idealism (i.e. Reality in the internal world of the subject). Instead it mediates these extremes and posits the necessary existence of both subject and object, not from a dualist position, rather, the two merge such that their outlines blur.
Impressionism aims at becoming the reproduction of one impression on the artist's eye, and through his eye on his mind.
Impressionism is a way of seeing reality with a primitive eye, of seeing reality in the living atmosphere of forms, decomposed, refracted, reflected by beings and things, in incessant variation.
Impressionism is a medium of feelings, a style of suggestion rather than of representation.
Impressionism is objective, merely painting what one sees divorced from personal experience and cultural conventions.
Impressionism is a primitive way of looking at the world. The impressionist artist is one who, forgetting the pictures amassed through centuries in museums, forgetting his optical art school training line, perspective, color by dint of living and seeing frankly and primitively, paints as simply as he sees.