Appreciation（欣赏） of sculpture depends upon the ability to respond to form in three dimensions（方面;[数] 维）. That is perhaps why sculpture has been described as the most difficult of all arts. Certainly it is more difficult than the arts which involve appreciation of flat forms, shape in only two dimensions. Many more people are "form blind（瞎的）" than "color blind（瞎的）". The child learning（学习） to see first distinguishes（区别） only two-dimensional（空间的） shape. It cannot judge distances, depths（[海洋] 深度）. Later, for its personal safety and practical needs, it has to develop, partly（部分地） by means of touch, the ability to judge roughly（粗糙地） three-dimensional（空间的） distances.

  But having satisfied（令人满意） the requirements（需要） of practical necessity（需要）, most people go no further. Though they may attain（达到） considerable（相当大的） accuracy（准确(性)） in the perception of flat form, they do not make the further intellectual（智力的） and emotional（感情的） effort needed to comprehend（理解） form in its full spatial existence.