As I understand it, Kantian constructivism is partly a position in normative ethics and partly a position in metaethics. In metaethics, it is the position that ethical claims have truth values, but their truth conditions consist not in a set of objective facts to which they correspond, but instead in the outcome of some procedure of deliberation resulting in decisions about what to do.

What Smith and Marx have in common is that they were both philosophers of great vision and perceptiveness, deep humanity, and a sense of social reality that has been lost in the abstractly formalistic economic theories that have dominated the field since the last third of the nineteenth century.

There is no author or legislator of the moral law. It is simply valid in itself in the nature or essence of things. We become autonomous only when we obey it, because then our will aligns itself with the objectively valid law, and our choice follows the same law as that we give ourselves. We can think of rational faculty (or the idea - the pure rational concept, not exhibitable in experience) as the legislator or author of the law because reason recognizes an objective standard, and to that extent is already aligned with objective moral truth.

As Kant says, the contribution of any common laborer would be greater than that of the greatest philosopher unless the philosopher makes some contribution to establishing the rights of humanity.

Some of Kant's particular moral opinions, either because he shared the prejudices of his time, or because of his own personal crotchets, can strike sensible people as ridiculous or offensive. But in my view, his own theory provides us with the resources (the best resources available, I believe) to correct his own personal errors or cultural prejudices.

Kant's system of duties constitutes a Doctrine of Virtue because the duties also indicate what kinds of attitudes, dispositions and feelings are morally virtuous or vicious.

It would be nice, wouldn't it? if we could get comfortable about the problem of freedom. Kant thinks that we can't.