Halliday & Matthiessen (2014: 384):
There is a long tradition of characterising such phenomena, in grammar books, as a list of very general categories, for example ‘persons, other living beings, objects (concrete or abstract), collectives, institutions’. These are relevant grammatically because they relate to a cline of potential agency — that is, the likelihood of functioning as Actor/Agent in the clause; the most likely being persons (human nouns), and the least likely being concrete objects.