The purpose of this paper is to develop Moral Dynamics which deals with the moving forces acting on our moral lives in the intergenerational Ethics. More exactly, it is to present On and Hope as the moving forces through complementing the work of Daniel Callahan and Hans Jonas, respectively. Callahan writes in his article "What Obligations Do We Have to Future Generations": "From our obligations to the past stems our obligation to the future". Obligation of the former is an English translation of on by Ruth Benedict, with a meaning of indebtedness. Obligation of the latter is used to mean the duty of repayment, its first priority being to provide the future generations with possibility of life and survival. However, while Benedict writes as "One makes part payment on on to one's parents by giving equally good or better things to posterity", Callahan made an erroneous citation as "past payment". This erroneous citation implies that Callahan overlooks the idea of "Repaying One-Ten-Thousandth", which means that benefit from the past can enerzize the lives of repayment persistently because of its infiniteness. Therefore, On should be reconstructed as the concept of Moral Dynamics. Jonas writes in his work "Imperative of Responsibility" that his future-oriented ethics is not devoid of hope but gives fear its rightful place. Nevertheless, he expresses his idea on hope ambivalently in an interview in the "Spiegel". On the one hand, he states that one of the requisites to avoid catastrophe is not to abandon hope. This statement implies that he accepts the hope as a moral dynamic to bear the responsibility. On the other hand, he states that he finds a paradoxical hope in the situation that persons learn a lesson from catastrophe. Hope of this sort, however, can never be a force capable of rendering ethics feasible. In conclusion, ethics for future generations need not only the force of hope which pulls us towards the future, but also the one of on which pushes us based on the past.