Full Idea
Natural necessity involves causal directionality as an essential element, while entailment as a purely logical relation does not.
Gist of Idea
If explanation is by entailment, that lacks a causal direction, unlike natural necessity
Source
Harré,R./Madden,E.H. (Causal Powers [1975], 7.V)
Book Reference
Harré,R/Madden,E.H.: 'Causal Powers: A Theory of Natural Necessity' [Blackwell 1975], p.134
A Reaction
If there is a naturally necessary relation between an eclipse and its cause, the directionality of that doesn't seem to arise from the mutual relation between the two. You have to add time's arrow, or causation's arrow.
Related Idea
Idea 15294 Powers can explain the direction of causality, and make it a natural necessity [Harré/Madden]