Full Idea
A barrier to the formulation of an energy conservation principle by early Newtonians was their lack of a notion of potential energy.
Gist of Idea
Early Newtonians could not formulate conservation of energy, having no concept of potential energy
Source
report of Isaac Newton (Principia Mathematica [1687]) by David Papineau - Thinking about Consciousness App 3 n5
Book Reference
Papineau,David: 'Thinking about Consciousness' [OUP 2004], p.239
A Reaction
Interestingly, the notions of potentiality and actuality were central to Aristotle, but Newtonians had just rejected all of that.