Which agents are human?

Question

The agent of a passive construction is in ablative, and human agents also come with the preposition a/ab. For example, Marcus a Gnaeo occisus est but Marcus sica occisus est. But which agents should be considered human?

Many cases are clear, but there are also less obvious situations. For example, are gods, dolls, anthropomorphic robots and pets with human-like status human? My Latin grammar gives the example A Deo mundus creatus est, implying that the Christian god can be viewed as human — without implying that it would always be viewed so.

Can you give some guidelines for choosing which agents to consider human and which ones non-human? I would prefer the guidelines to be backed by classical usage or a reliable grammar book.

Answer 1

Ovid's Remédia Amórés 422 suggests that your grammar is mistaken and that non-humans with agency can be considered agents:

Á cane nón mágnó sæpe tenétur aper.

Cicero's Dé Officiís 1.68 suggests that, at least metaphorically, emotions can be considered agents:

Nón est autem cónsentáneum, quí metú non frangátur, eum frangí cupiditáte, nec quí invictum sé á labóre præstiterit, vincí á voluptáte.

What I take from these examples, along with others, such as this from Livy III.37, which suggest that humans can be instruments—

Et decemvirí, quí prímó tribuniciós hominés, quia id populáre habebátur, circum sé ostentáverant plebí, patriciís iuvenibus sæpserant latera.

—is that, pace nineteenth-century grammarians, we are permitted to and indeed must decide for ourselves, when determining what construction to use, whether any given noun is functioning as an agent or an instrument—that is, whether it is exercising its will (agent; use the preposition) or being used by something else that is exercising its will (instrument; omit the preposition).

Answer 2

I think there is a semantic difference between "a Gnaeo" for the agent and "sica" for the instrument. The agent will be expressed in this way only in a passive sentence, but the ablative of instrument can be used also in an active sentence (Marcum sica occidit). The agent is normally animate. Note that there is a difference between "animate" (=humans, gods, animals), "rational" (=humans and gods, but not animals) and "human".