In English, the preposition by is used as agent preposition. This means, that when you transform an active sentence, such as this –
The callous criminal murdered the poor beggar
into a passive one, the subject of the active sentence is pointed out using the preposition by:
The poor beggar was murdered by the callous criminal.
People tend to think that the Irish preposition ag always corresponds to the English preposition by in passive constructions. This is of course basically correct, but only to a certain extent. To start with, what does “passive” mean in grammar?
In an active sentence, such as “The callous criminal murdered the poor beggar”, the agent of the action (the callous criminal) is also the subject of the sentence. If we substitute “he” for “the callous criminal”, we get “He murdered the poor beggar”. “He” is the subject form of the pronoun. On the other hand, if we substitute a pronoun for “the poor beggar”, we get “The callous criminal murdered him”. Here the form is “him”, an object form. Thus, the patient or “sufferer” of the action is in the object position and takes the object form.
In a passive sentence, the patient, though, is in the subject position, and the agent can be left completely unmentioned:
The poor beggar was murdered
or mentioned in a prepositional phrase, the preposition being by in English:
The poor beggar was murdered by the callous criminal.
I hope you have now understood the idea. By the way, the grammatical category that can be passive or active is called voice or, in a more learned way, diathesis. Back when all learned men were men and spoke Latin, the term genus verbi (the “gender” of the verb) was also used. In German, we also use Handlungsrichtung, “the direction of the action”, which makes eminent sense, but regrettably, English seems not to have an equally good term. In Irish, “voice” in this sense is faí (it’s feminine: an fhaí, genitive na faí), “active voice” being an fhaí ghníomhach, “passive voice” called an fhaí chéasta.
Now that you should know what we are talking about, let’s get on with the Irish-language part of the story.
It is basically true that in Irish, the agent of an action or a development takes the preposition ag. Thus, we have such constructions as: tá mo chroí briste agat “you have broken my heart”, or even tá a chuid gruaige liath ag an aois “his hair is grey with old age” (word for word, “grey by the age” – note that Irish uses article for generic, abstract things, while English does not). And of course, in tá sé á bhualadh ag na ruifínigh “he is being hit/beaten by the ruffians”, we have an obviously passive construction with ag marking the agent.
In Irish, there are two kinds of passive constructions: the situational passive or Zustandspassiv, as Germans say, and the progressive passive. The situational passive is created by combining a finite form of the verb tá “is” and the participle of the verb: déanta, críochnaithe, briste, scríofa, faighte, and so on. It is appropriate to use the German term Zustandspassiv for Irish, because this construction is used in a way similar to the German one: it suggests that the action is already finished, and the result has been attained:
Tá mo chroí briste agat. “You have broken my heart. My heart has been broken by you.”
Tá an tasc críochnaithe ag an oibrí. “The worker has finished the task. The task has been finished by the worker.”
Tá an t-úrscéal scríofa ag an údar. “The author has written the novel. The novel has been written by the author.”
Note that although this Irish construction looks similar to the English one – “The book is written by the author” – its meaning is quite different. The English construction suggests an ongoing process, while the Irish one suggests a finished one.
In Irish, we have another passive construction, the progressive passive, which suggests ongoing activity (“progression”). Thus:
Tá an t-úrscéal á scríobh ag an údar “The novel is being written by the author”.
Here, we have a form of the verb tá combined with á + verbal noun. It can also be written dhá or dá (actually, I have no idea whatsoever which of these is the official standard, and could not care less). Anyway, this is a combination of do + possessive pronoun, in this particular instance the third person possessive pronoun a “his, its”. Thus, tá an t-úrscéal á scríobh means, word for word, “the novel is to its writing”.
Note that the do can in this construction combine with other possessive pronouns, too:
tá mé do mo thuirsiú ag an múinteoir “I am being exhausted/bored by the teacher”
tá tú do do thuirsiú ag an múinteoir “you are being exhausted/bored by the teacher”
tá sé á thuirsiú ag an múinteoir “he is being exhausted/bored by the teacher” (also dá thuirsiú or dhá thuirsiú)
tá sí á tuirsiú ag an múinteoir “she is being exhausted/bored by the teacher” (also dá tuirsiú or dhá tuirsiú)
tá muid dár dtuirsiú ag an múinteoir “we are being exhausted/bored by the teacher” (also dhár dtuirsiú; I recommend against using ár dtuirsiú here, because this ár can be confused with the pronoun ár “our”, which is combined with do in dár, dhár. However, don’t be confused if you do see ár in this position.)
tá sibh do bhur dtuirsiú ag an múinteoir “you guys are being exhausted/bored by the teacher”
tá siad á dtuirsiú ag an múinteoir “they are being exhausted/bored by the teacher” (also dá dtuirsiú or dhá dtuirsiú)
Note that in a combination of preposition and possessive pronoun (also called possessive adjective by Irish grammarians) the possessive pronoun comes last and determines, which initial mutation the verbal noun takes. Thus: do mo, do do lenite (t > th), á lenites when it includes a “his”, does not lenite (but adds h- to a vowel) when it includes a “her”, and it eclipses when it includes a “their”. Dár and do bhur eclipse.
So, in Irish there are two kinds of true passive constructions. However, when you hear “Irish” and “passive”, you probably think of the verb form known as saorbhriathar or the autonomous verb, which (for a regular verb) has the following forms:
present: dúntar, osclaítear
past: dúnadh, hosclaíodh
conditional mood: dhúnfaí, d’osclófaí
habitual past (imperfect past): dhúntaí, d’osclaítí
future tense: dúnfar, osclófar
There is an irritating habit among grammarians to equate this form with “passive”. This is wrong, because the formal difference between it and a real passive is obvious. In a real passive construction, the patient of the action becomes the subject of the sentence. This does not happen in the Irish autonomous form. As you should know, Irish third-person pronouns have object forms: sé, sí, siad become é, í, iad. Like this:
Bhris an buachaill an fhuinneog “The boy broke the window” – Bhris an buachaill í. “The boy broke it” (í, because fuinneog “window” is feminine).
Bhris an fear an buidéal “The man broke the bottle” – Bhris an fear é. “The man broke it.” (é, because buidéal “bottle” is masculine)
Bhris an buachaill na fuinneoga “The boy broke the windows”. – Bhris an buachaill iad “The boy broke them”.
These object forms are also used after the autonomous form. See:
Briseadh an fhuinneog – Briseadh í. “Somebody broke the window. Somebody broke it.”
Briseadh an buidéal – Briseadh é “Somebody broke the bottle. Somebody broke it.”
Briseadh na fuinneoga – Briseadh iad “Somebody broke the windows. Somebody broke them.”
So, the point of using the Irish autonomous form is not so much that of focusing on the patient rather than the agent, it is above all hiding the agent. This is why I translate briseadh na fuinneoga as “somebody broke the windows” rather than “the windows were broken”.
However, you do see the autonomous form used with an ag agent. My impression is, that it is much more common in bureaucratic and/or non-native Irish than in the works of native writers – indeed so common that it is a dead giveaway of non-native Irish. You do sometimes see it in native literature – one book that is almost to a non-native extent replete with it is Domhnall Mac Síthigh’s Fan Inti. (I am not recommending against the book, though, because it is very interesting in providing the reader with much important information about traditional boat-making – if you read it, you’ll learn all the boating terminology in Kerry Irish, which is quite a worthy undertaking for any Irish-language enthusiast). However, usually there is no ag agent added to the autonomous form – even in today’s Irish. a typical book by a native writer includes one or two instances. This suggests to me that the usage is basically Anglicist and very untypical of native Irish.
The Ó Donaill dictionary, which is not unnecessarily purist at all – in fact it includes a lot of loan words from English often attacked by purists – does not acknowledge ag as an agent preposition used with the autonomous verb, while it acknowledges other agent usages of the preposition. However, Ó Donaill notes that the preposition le can be used to refer to the agent of an autonomous verb, but only in older, pre-20th century literature (as the abbreviation Lit: suggests, in the dictionary).
Should this usage of le be revived? I am not sure. I have seen one or two instances of it used in this way in Gaeltacht literature, but it is so rare as to be almost as grating as ag, It should however be noted that it is still part of the living language in Gaelic Scotland, and the contemporary writer in whose works I have spotted it – a minor Donegal poet and seanchaí – might have learnt it over there.
There is also ó. I have been reliably informed that ó is sporadically used as agent preposition with autonomous verbs in Connacht dialects. However, this usage has, as far as I know, never entered native literature or folklore.
My opinion is, thus, that impersonal autonomous forms should never take any kind of agent constructions, and they should only be used when we don’t want, or when we don’t find it necessary, to mention the agent of the action at all.