Estar is for transient states or locations. Ser is for intrinsic properties. Being "for the captain" is part of what makes that soup that soup.
Does anyone have a link to a good explanation of por vs para? It's still difficult for me
This sentence would never be used in everyday life. Nor the last one: "The priests write books." Can duolingo create sentences that regular people would need in real life situations? I am grateful duolingo is free, but it could be improved.