Agency in Grammar
How information about agency or causation is encoded in different grammatical strategies
Languages have three ways of showing agency:
1) word order
2) case system
3) voice system.
A case system is what happens when a language puts the onus of bearing information about agency on the nouns. An example of a language that developed this grammatical strategy is Latin. In contrast, a voice system is what happens when it is the verb which becomes morphologically sophisticated in order to carry information about agency. An example of such a language with voice is Malay.
In English, grammatical case still exists only as vestigial feature in the pronouns, unlike Latin or Old English where all the nouns must have nominative case and accusative case. To simplify what I mean by case, the nominative case indicates the doer while the accusative tells you who the doee is.
I wed thee.
Thee I wed.
Wed thee I.
Word order is useless in a case system since all three sentences mean the same thing when the case system clearly marks the firstperson pronoun as nominative (doer) and the secondperson pronoun as accusative (one being done to = doee).
To reverse the action, you just switch the cases (instead of the order).
Thou wed me.
Me thou wed.
Wed me thou.
To show the direction of causation, the verb remains unchanged but the nouns undergo case declension. The nominative acts on the accusative. The opposite strategy to keeping the verbs unchanged, would be to keep the nouns (and word order) fixed, but to change the verb instead in order to show a change in causal direction.
In English it's a bit ugly but it looks like this:
Dog eats god.
Dog is eaten by god.
[eats] is the active voice of the verb eat. Dog is the agent (doer).
[is eaten by] is the passive voice of the verb eat. Dog is the patient (doee).
By changing the voice of the verb, you can change the direction of causation. English is a weird language because it has a vestigial case system for its pronouns but uses the voice system for pretty much everything else. And yet, English passive voice is so ugly because [is eaten by] is not one word.
Passive voice in english is not elegant but as a native speaker you would be forgiven if you had considered that this is a limitation of passive voice itself rather than a design flaw in the language specifically.
In Malay, there is just one word for the passive voice and another monolexeme for the active voice. Malay, therefore, has a much more elegant (and dare I say more sophisticated) voice system than English but word order is much stricter otherwise it would be confusing for the active and passive voice of the verb to determine which noun is the agent and which is the patient.
To summarize, languages have three ways of showing agency:
1) word order
2) case system
3) voice system.
Latin uses 2. Malay uses 3 + 1. English is a mix of all three strategies.