it is a &quot;model-theoretic&quot;
relation, or else a &quot;proof-theoretic&quot; relation, or both, at least, to the extent
that one can have both.

JA: It hertz me to have to say it,
    But I'm afraid that I observe
    A defect in the picture given.
    Arrows of logical implication
    And arrows of cause to effect
    Need not of necessity commute
    These all too convenient ways.

HP: This is a misunderstanding, not a defect.  Hertz's &quot;consequent&quot; means 
    only &quot;following&quot; in