The view that the world is developing forever was illustrated by Engels in his many writings. According to Engels, development is forever because of its infinity. And first, this infinity is a kind of potential infinity as well as the infinite continuity and infinite separability. Secondly, it also a kind of actual infinity which is the end of the history. The two kinds of infinity are heterogeneous, incoherent or contradictory. Engels knew this absurdity and used it to criticize Hegel. But Engels used Hegel's view about qualitative change and quantitative change to solve this problem in his own theory. Actually, Hegel criticized the potential infinity and did not think that potential infinity can become actual infinity. Therefore the Engels criticized Hegel wrongly and his own view of development was also wrong.