不好意思，想请问Genitive与ablative of Description两者之间的差别？
什么时候用前者，什么时候用后者？
A Primer of Ecclesiastical Latin上的例子：
1.Genitive
Sumus populus misericordiae?
Primi Christiani erant homines laeti animi.
2.Ablative
Petrus erat vir magna anima.
Gratia.

Ablative Description, especally of physical qualitiesGenitive Descri, especally of Non-physical qualities以上，来自Cambridge Latin Grammar, page53, 50