"Paint studies of parts, for instance a piece of land, a group of trees or things like that, but always in a way that people can understand these things in relation with the whole landscape, by adding behind that group of trees the air in a right tone color and thereby in connection with the trees.. .Furthermore studies of a whole, preferably very simple subjects - A meadow with horizon and a piece of air to examine further the general tone color, the harmony of the whole.. ..and study nature even more by thinking about it than working after it. (translation from original Dutch: Fons Heijnsbroek)"