Full Idea
Newton's Third Law implies the conservation of momentum, because 'action and reaction' are always equal.
Gist of Idea
Newton's Third Law implies the conservation of momentum
Source
report of Isaac Newton (Principia Mathematica [1687]) by David Papineau - Thinking about Consciousness App 3
Book Reference
Papineau,David: 'Thinking about Consciousness' [OUP 2004], p.239
A Reaction
That is, the Third Law implies the First Law (which is the Law of Momentum).