Agents of passive predicates in Greek are realized either in the dative case or with a prepositional phrase. Standard doctrine holds that the realization of the agent phrase is conditioned by grammatical aspect ([2, p. 422], [3, p. 150.2], [4, §§1488, 1490], [1, pp. 1, 78]). Dative agents are licensed by perfect passive predicates, while prepositional phrase agents occur elsewhere:
(1) i. ἡ δὲ ὁδὸς ἡ ἡμερησίη ἀνὰ διηκόσια στάδια συμβέβληταί⸗μοι.
‘A day’s journey has been calculated by me at 200 stades.’
ii. οἱ ὑπ’ αὐτῶν ἐξεταζόμενοι ἐμοὶ ὀργίζονται.
‘The ones that get questioned by them get angry at me.’
Pl. Ap. 23c8–23d1
In (1), we have an example of a dative agent with the perfect (1i). In (1ii), the predicate is a present imperfective participle and the agent is realized with a prepositional phrase, as expected.
Counterexamples to this generalization run in both directions, however:
(2) i. λέγεται δὲ τοῦδ’ ἕνεκα ταῦθ’ ἡμῖν, ὡς...
‘These things are said by us for the following (reason), that...’
ii. ἐξεληλαμένος τε ὑπὸ τοῦ πατρὸς...
‘And having been banished by my father...’
In (2i), the dative pronoun ἡμῖν with a present imperfective. In (2ii), the perfect participle ἐξεληλαμένος occurs with a prepositional phrase agent ὑπὸ τοῦ πατρὸς.
George  argues that dative and prepositional phrase agents are licensed under the following conditions:
(3) Dative of agent
i. Perfect predicate
ii. Inanimate subject
iii. Pronominal agent
iv. Finite verb
(4) Prepositional phrase agent
i. Non-perfect predicate
ii. Animate subject
iii. Nominal agent
Quantitative analysis reveals that George’s model offers only a marginal improvement over the standard model.
In this paper, I argue on the basis of a sample of 441 tokens of passive predicates with overt agent phrases from Herodotus’ Histories that the following factors are better predictors of dative agents:
(5) i. Agent is clitic pronoun
ii. Subject bears the theme semantic role
iii. Predicate is aspectually perfect
Subjects bearing the theme semantic role exhibit one of two properties: they are either brought into or out of existence by the event or they undergo involuntary movement. In other words, the subjects are undergoing an involuntary change of state. The association with the perfect means that this change of state is relevant to the current discourse. The agent of such an event should correspondingly be well established in the discourse, which is why dative agents are so often realized as clitic pronouns. ese three properties cluster together because they are characteristic of events involving high subject affectedness.
The dossier in (5) is not a list of necessary and sufficient attributes that a clause must possess for a dative agent to be licensed, however. If a clause has all three properties, it is highly likely that the agent will be in the dative case. Figure 1 reveals that clauses with only two of three properties in (5) are also highly likely to have a dative of agent as opposed to a prepositional phrase agent.