A.H. Barr said in his Picasso 50 years of his art in relation to the formation of Picasso's blue period : "Just why Picasso came to use so much blue over so long a period has never been convincingly explained." The question "why Picasso came to use the specific shapes in this period " hasn't also been satisfactorily answered. These questions are concerned not only with the formation of Picasso's one epoch, but also with the basis of his artistic activity itself. They often say that Picasso changed with bewildering rapidity. And everytime Picasso changed the appearence of his works, certain influences were supposed for the reason of these changes. So they searched for the forms which are similar to Picasso s, in many other works. Certainly Picasso's works show occasional resemblance to other ones' from pre-historic to contemporary. And these resemblances are regarded as the effects of influences from these works on Picasso. But resemblance doesn't always mean influence. Because Picasso often used other artists' works just for a starting-point of his creation. And each relationship between Picasso's works and ones of other artists differs in quality. Some works became a pretext of Picasso's creation even keeping visible resemblances in his works, and some works gave orientation to his plastic activity even losing visible resemblances thouroughly. Therefore, the most important thing must be to find out what determined and brought up Picasso's artistic activity.