And it is necessary that the signs, whether shadow or substance, should be completely painted as they appear to the eye in nature when observed with average care by one inspecting a view for the purpose of drinking in all its beauties, for this is how a painted landscape is usually examined. There is no place in the painter's art for a suggestive sign in the sense that it may suggest a required complete sign. A sign must be painted as completely as possible in conformity with its appearance as seen from the presumed point from which the artist sketched his view, for the reason that its value as a sign depends upon the readiness with which it is understood.[63] This is incontrovertible, otherwise the art of painting would be an art of hieroglyphics. In poetry suggestion is of great importance, and it may be so glowing as to present to the imagination a higher form of beauty than can be painted; but the signs of the painter cannot suggest beauty in this way, because the exercise of the imagination in respect of them is limited by their form. A sign painted less distinctly than as it is seen in nature is obviously removed from its proper relative position, or else is untrue, and in either case it must have a weakening effect upon the picture. The successful representation of aerial perspective depends upon the careful and close gradation of tones in conformity with the varying atmospheric density. This is difficult work because of the disabilities arising from the reduction of the scene into miniature form, which necessitates the omission of many tones and effects found in nature, just as a portrait in miniature involves the exclusion of various elements of expression in the human countenance. But fortunately in landscape the variableness of nature greatly assists the artist. Only rarely is the atmosphere of equal density over a considerable depth of ground, and this fact enables the painter to simplify his work in production of the illusion without appearing to depart from nature. Thus he may deepen or contract his foreground within wide limits. The changes in the appearance of the atmosphere in nature have to be greatly concentrated in a painting, and as this concentration becomes more difficult as distance is reached, it follows that the artist has a better chance of success by making the foreground of his picture begin some way in front of him, rather than near the spot where he is presumed to stand when he executes his work. He may of course maintain some very near ground while materially shortening his middle distance, but this method must obviously lower the beauty of the painting as a distance landscape, and make the execution vastly more difficult. Claude adopted this plan sometimes, but it is seen in very few of his important works. In his best time Turner was careful to set back his foreground, and to refrain from restricting his middle ground.