# Are there any direct comments by Isaac Newton on Leibniz's living force / vis-viva?

The living force or the vis-viva is a quantity usually attributed to Leibniz (although there were a few other people who identified it as a conserved quantity in certain collisions earlier). Many accounts say that there was tension between Leibniz's work and Newton's work, and in particular there was tension between conservation of vis-viva and Newtonian mechanics. (Of course, we now know there is no tension between the two things.)

However, I couldn't find any specific comments by Isaac Newton on the concept of Leibniz's vis-viva. Are there any quotes by Isaac Newton himself where he explicitly rejects this notion as meaningful? Does he ever make any reference to it?

[...] Leibniz’s 1686 note provoked exchanges with the Cartesians. Descartes’ conservation of motion (see figure 1) was difficult to abandon if one believed that all space is filled with matter. The exchanges led Leibniz to refine his position in writings on “dynamics” (the term is his) that were not published until the 19th century. In those writings Leibniz grants the conservation of directional motion, but argues that because it is directional, unlike $$mv^2$$, it involves reference to other bodies and therefore is not a feature of each body taken unto itself. He concedes that $$mv^2$$ is not obviously conserved in the collision of soft bodies. But he contends that it is actually conserved via undetected motion of the microphysical parts of the bodies...