In Mini Story Russian 41 we see three forms meaning “hungry”:
друг алана был не очень голоден
друг алана был голодный ?
нет. друг алана был не очень голодным
голоден – the so called Краткая форма
голодный – the nominative case
голодным – the instrumental case.
Why is the instrumental case not used in the second sentence? Or are we free to use the nominative case or the instrumental case in this kind of sentences?
It seems to me that this could have been written more concisely if it is even correct. This looks very confusing.
The nominative and instrumental cases can be used interchangeably in predicate nominal and predicate adjective clauses. The verb быть usually takes instrumental case in future and past forms, and nominative case in the present. Theoretically, the nominative applies to permanent conditions and the instrumental applies to temporary states, but I doubt that anybody really cares about that difference in casual speech.
That is a clear explanation! Thank you, Bautov!