Question

Good evening!
1. At first glance, Hume’s claim that one cannot derive an ought from an is assumes that there are no “Ideas” in reality, since that is precisely his claim—that because one cannot observe Ideas, both science (induction) and ethics are products of the structure of the human being himself, and are not claims about the world (and are equivalent to the claim that I should eat because it is moral. That is, it is not morality that makes a demand on the person, but a need).
In other words, one cannot speak about values unless they are objective Ideas external to reality (transcendent), and certainly not if they are composed of the facts of reality.
If so, it is difficult for me to understand how Aristotle, who denied the existence of Ideas beyond reality, was able to establish a binding ethics. After all, Hume is right that one cannot speak of value on the basis of the existence of facts alone (that is, the non-existence of Ideas)?
2. Kant argues that a person ought to be rational. My difficulty is: why? Is it because this is a way to live well? Meaning, just as someone might tell me what the best way to eat is. Or is there something more to it? In other words, self-realization is more than a description of the existence of a fact (after all, we do not say of someone who has the potential to eat and does so that he has realized himself—unless, of course, we are being cynical…)?
3. Likewise, Kant argued that ethics derives from morality. What is the connection?
Thank you very much!