Originally Posted By: Finiter
If the third law is taken as a physical law, then it is not clear where the action and reaction are. Newton has not stated whether the same body will be subjected to both action and reaction, and whether the action and reaction happens at the same time.


There is a certain thread of logic here. Newton was talking about the motion of bodies, perhaps he assumed that his readers would make the connection. In any case, an action, without a subject and object (in the grammatical sense) is a non-entity; it would be like talking about a shadow that had no object (in the physical sense) to cast it, and no surface on which to be cast. Would there still be a shadow?

As for the question of “whether the same body will be subjected to both action and reaction”; the action/reaction relationship, in this context is meaningful only if applied to the same body. If the “reaction” is applied directly to another body, it has to be regarded as an “action” in its own right. If you don’t accept this, then you have to consider whether your initial action occurred as a result of something else, and was therefore a “reaction”. This would lead you into an infinite regression situation, which would tend to paralyse scientific thought.

There never was nothing.