When using "to be"...
When you use sein (to be) in German, do you have to turn a following noun to accusative. For example, for "The animal is the dog", is it "Das Tier ist ein Hund" or "Das Tier ist einen Hund". Danke!
Das Tier ist der/ein Hund is straight up nominative. Nobody doing anything to the dog, it's not the object of any action whatsoever, neither directly nor indirectly. It just is. That's what the nominative was invented for; it's the poster child of a nominative sentence, if you will ;-)
Ich füttere einen/den Hund is accusative. I am doing something to the dog - feeding it - which turns it into the direct object of my action.
Ich gebe dem/einem Hund den Ball Now the dog is the indirect object - it is being given a ball by me - which requires the dog to be in the dative case.