No theory about our bodies as mere objects of observation and calculation (as distinct from partners in communicative interaction, assumed to be free) can comprehend human nature.

One rational standard of action is how well it promotes the end it seeks. Another standard is whether it aims at ends which are good. Both of these, but especially the former, depend on judgments of fact.

We can't coherently deny, or even decline to affirm, that we are free.

Kant does represents a distinctively modern view of the human condition in contrast to that of ancient high culture, found in ancient Greek ethics and also in ancient Chinese ethics.

Kant does not think there is anything wrong with being beneficent from sympathy. He thinks we have a duty to cultivate sympathetic feelings by participating in the situations of others and acquiring an understanding of them. He thinks we also have a duty to make ourselves into the kind of person for whom the recognition that something is our duty would be a sufficient incentive to do it (if no other incentives were available to us). That's what he means by "the duty to act from the motive of duty".

Fichte thinks that the mutual recognition of one another as free beings belongs among the transcendental conditions of self-consciousness itself.

Fichte would identify all states of our minds with states of our body - perhaps not merely of our brain, but the whole body as an acting organism.