Consider any instance of reasoning, for example the case of the abbe and the squire. "Ladies", says the abbe, "do you know that my first penitent was a murderer?" "Ladies,", says the squire, entering shortly afterward, "do you know that I was the abbe's first penitent?"
Of course a conclusion was produced in the ladies' minds, and the question is about the nature of the causation that produced it. Now the ladies' entertainment of the premises had something causally to do with the emergence in their minds of the conclusion. The question is whether, when we say that the one contributed causally to the other, our only proper meaning is that whenever the first appears the second one does, or whether we must also say that the special logical relation in which the content of the premises stands to the content of the conclusion had something to do with the appearance of that conclusion. It did have something to do with it.
According to the regularity theory, our only reason for expecting the judgment that arose rather than some other judgment, such as that Florida raises grapefruit, is that thoughts of the first kind have regularly been followed by thoughts of the second. The question why what followed did follow is one which we cannot answer. The connection between the events is no more intelligible than the connection of lightning and thunder for a savage.
If the ladies were asked how they came to have the belief, they would say that it was because this belief was implied by what they were thinking in the previous moment, and this is the natural and correct answer. Other causes could have contributed to the result. We are not saying that causality reduces to logical necessity. But when one passes in reasoning from ground to consequent the fact that the ground entails the consequent is one of the conditions determining the appearance of this consequent rather than something else in the thinker's mind.