The practice of presenting nude with clothed figures where the subject does not absolutely compel it, is commonly supposed to be for the purpose of contrast. This may have been the object in some cases, but in very few is the interest in the contrast not outweighed by the bizarre appearance of the work. As a rule in these pictures there is nothing in the expressions or actions of the personages depicted to suggest a reason for the absence of clothes from some of them, and so to the average observer they form a "problem" class of painting. The first important work of the kind executed was Sebastiano del Piombo's Concert, in which the group consists of two nude women, one with a reed pipe, and two men attired in Venetian costume, of whom one handles a guitar.[a] The figures are very beautiful and the landscape is superb, but as one cannot account for the nude figures in an open-air musical party, the æsthetic value of the work is largely diminished. This painting has suggested several designs to modern artists, the most notable being Manet's Déjeuner sur l'Herbe, where a couple of nude women with two men dressed in modern clothes are shown in a picnic on the grass. Not only is the scheme inexplicable, but the invention is so extravagant as to provoke the lowest of suggestions. In a composition of this kind only a great artist can build up a harmonious design. [a] At the Louvre. Formerly attributed to Giorgione. Titian's picture known as Sacred and Profane Love,[a] where the figure of a nude woman is opposed to one clothed, may really signify any of a dozen ideas, but the artist probably had no other scheme in his mind than to represent different types of beautiful women. Crowe and Cavalcaselli's suggested title of L'Amour ingénu et l'Amour satisfait, was certainly never conceived by Titian, nor is Burckhardt's proposal, Love and Prudery, possible in view of the flowers in the hand of the draped figure. In any case this picture is the greatest of its kind, for the composition is so delicate and harmonious, and the art so perfect, as to render its precise meaning a matter of little consideration. Another picture of Sacred and Profane Love was painted by Grien.[b] He shows a nude woman from whom Cupid has just drawn the drapery, and another woman concealing her figure with loose drapery. The effect is weak. The nude figures in the well-known Drinkers of Velasquez[c] are undisturbing because they are not very prominent in the picture, but their significance is not apparent. [a] Borghese Gallery, Rome. [b] Frankfort Museum. [c] The Prado, Madrid.