My understanding is that Kant grounds the practical belief in human freedom on the universal fact of moral responsibility. — Janus
Another good point, and relates to what you said about Hume’s simplistic thinking. Hume was an empiricist, which makes explicit the principle of cause and effect be paramount in his thinking. From that, comes this:
“....It appears that, in single instances of the operation of bodies, we never can, by our utmost scrutiny, discover any thing but one event following another, without being able to comprehend any force or power by which the cause operates, or any connexion between it and its supposed effect. The same difficulty occurs in contemplating the operations of mind on body- where we observe the motion of the latter to follow upon the volition of the former, but are not able to observe or conceive the tie which binds together the motion and volition, or the energy by which the mind produces this effect. The authority of the will over its own faculties and ideas is not a whit more comprehensible: So that, upon the whole, there appears not, throughout all nature, any one instance of connexion which is conceivable by us. All events seem entirely loose and separate. One event follows another; but we never can observe any tie between them. They seemed conjoined, but never connected. And as we can have no idea of any thing which never appeared to our outward sense or inward sentiment, the necessary conclusion seems to be that we have no idea of connexion or force at all, and that these words are absolutely without meaning, when employed either in philosophical reasonings or common life....”
(WSM, 1737)
“.....It is God himself, who is pleased to second our will, in itself impotent, and to command that motion which we erroneously attribute to our own power and efficacy....”
(EHU, VIII, 1748)
Hume couldn’t conceive a natural connection between the “authority of the will over its own faculties”, therefore he was left without a cause for a given effect, anathema to an empiricist but sufficient for a sentimentalist. We don’t know whether he threw out the concept of freedom, or never even thought of it to begin with, but the point is, he stopped short, philosophically. Perhaps the shadowy ghost of infinite regress curtailed his intelligence....dunno. Left it to the heavens, he did.
Kant, an the other hand, granting Humian cause and effect in the physical world as given, thus recognizing the need for consistency of the principle with respect to the authority of the will in a possible metaphysical context wherein your “universal fact of human responsibility” is an effect and presupposes a necessary cause. But he was still at the mercy of infinite regress, for to suppose freedom as a cause necessitates it be at the same time an effect. What Hume didn’t consider is this:
“....I adopt this method of assuming freedom merely as an idea which rational beings suppose in their actions, in order to avoid the necessity of proving it in its theoretical aspect also. The former is sufficient for my purpose; for even though the speculative proof should not be made out, yet a being that cannot act except with the idea of freedom is bound by the same laws that would oblige a being who was actually free. Thus we can escape here from the onus which presses on the theory. We have finally reduced the definite conception of morality to the idea of freedom. This latter, however, we could not prove to be actually a property of ourselves or of human nature; only we saw that it must be presupposed if we would conceive a being as rational and conscious of its causality in respect of its actions, i.e., as endowed with a will; and so we find that on just the same grounds we must ascribe to every being endowed with reason and will this attribute of determining itself to action under the idea of its freedom...”
In short, Hume couldn’t prove a cause, Kant showed no proof was necessary. We couldn’t tell the difference between a rational being with freedom theoretically proven as cause for the authority of the will, from a rational being with merely the presupposed idea of freedom as the means for the authority of the will.
TA-DAAAAAA!!!!