Full Idea
Russell call 'if...then' implication, when the material conditional is a much better account; C.I.Lewis (in founding modern modal logic) preserved Russell's confusion by creating 'strict implication', and called that implication.
Gist of Idea
Lewis's 'strict implication' preserved Russell's confusion of 'if...then' with implication
Source
comment on B Russell/AN Whitehead (Principia Mathematica [1913]) by Willard Quine - Reply to Professor Marcus p.177
Book Reference
Quine,Willard: 'Ways of Paradox and other essays' [Harvard 1976], p.177
A Reaction
[A compession of Quine's paragraph]. All of this assumes that logicians can give an accurate account of what if...then means, when ordinary usage is broad and vague. Strict implication seems to drain all the normal meaning out of 'if...then'.