Errol E. Harris, Formal, Transcendental, and Dialectical Thinking: Logic and Reality (SUNY Press, 1987), pp. 38-39:
Sometimes an excuse is offered for the paradoxical (one might say, illogical) character of material implication on the ground that the Philonian interpretation of the conditional is the weakest which will satisfy the requirement that the rule of detachment gives a valid inference. But it is obvious from the foregoing that it does not satisfy this requirement; for unless there is some essential connection between p and q we cannot validly argue "If p then q, and p; therefore q." We ought not even to assert, "If p then q" except on the condition that there is a connection between what the propositions express. The Philonian interpretation licenses the schema "If p, then q" whether or not there is any connection, so we might argue:
If pigs cannot fly, Socrates is mortal;
but pigs cannot fly,
therefore, Socrates is mortal.
Although this argument is valid according to the current doctrine, the conclusion, as long as it includes the word "therefore," is false, because it alleges in effect that the reason for Socrates' mortality is the flightlessness of pigs. Accordingly, we have an implicitly false conclusion from true premisses, and that is precisely what the rule of detachment is supposed to preclude.