The former is a personal sentence and the latter an impersonal one, though both the sentences seem semantically (almost) equivalent.
Concerning personal and impersonal sentences, I have some idea how different they are in the light of the speaker's consciousness, for example: In the case of "я хочу спать" vs "мне хочется спать".
But, in the case of the above two sentences, I don't have an idea how different. Please let me know what the difference is.
IMHO, the difference is logical emphasis.
In "Деревья свалил ветер" the wind is emphasized in order to show that it was not done by other force e.g. flood or human. The sentence base (основа предложения) is "ветер свалил".
In "Деревья свалило ветром" it is emphasized that the trees are fallen. The sentence base is "свалило".
“Деревья свалил ветер” - active. more frequetly used: Ветер свалил деревья.
English sentence order: Wind dropped the trees.
“Деревья свалило ветром” - frequently used correct form.
For better understanding: here is missed subject [Что-то/Нечто].
[Что-то] свалило деревья ветром.
English sentence order: [One/It/Something] dropped the trees by the wind (using wind).
“Деревья были свалены ветром” - passive, grammatically correct but unused))
English sentence order: Trees were dropped by the wind.
"Деревья свалились из-за ветра" - correct, used.
Trees have fallen (fell) due to wind.
Both "Деревья свалил ветер" and "Деревья свалило ветром" point at the reason why those trees don't stand anymore. I find no special emphasis on the wind vs. the trees here: the agent "ветер" takes emphasis in both versions. And without any additional context (like an opposed opinion about that 'reason') neither version expresses a stronger sense like 'It was the wind that kicked the trees down' (Именно ветер свалил деревья). So the difference between those two looks not too sufficient. But still, one can imagine a usage situation where some native speakers would prefer a particular version.
situation one:
- Why are those trees lying?
- It was windy last night, so the wind kicked the trees down.
(both Russian versions are possible here, the first one might slightly hint at the rescent windy weather)
situation 2 (phone talk, letter, etc.):
- Are those remarkable trees still alive?
- Not anymore. The trees were kicked down by the wind.
(the second Russian version is more natural here since some time has passed and there is no reason for mentioning the wind in more realistic manner, as the subject; however the first version wouldn't be a mistake here)
P. S. Considerations on usage of different prefixes in that verb: свалило vs. повалило. In both sentences in question I'd prefer "повалил(о)", probably because the action here is undefined directionally as opposed to сases like "свалило в кучу", "свалило с ног" (about a person; maybe due to some correlation with the preposition "с" here).
Roughly, I'd say it's a case of an implicit definite/indefinite distinction, similar to Я не видел её револьвер vs. Я не видел у неё револьвера. I feel that Деревья свалил ветер doesn't necessarily logically emphasise the wind as some suggested above; rather, it implies the action of what, in English, would be referred to as "the wind" rather than just "wind"; a particular instance of wind that was discussed before or is common knowledge.
Answering how looks like an idea what the difference is:
Like in geometry, we are able to build the diagonal in the given square when trying to solve a puzzle, the rebuilded "figure of speech" shall be allowed to us too.
First, we reorder the first sentence:
Subject-Verb Agreement = SVA
SVA SVA
┌──◄─►──┐ ┌──◄─►─────────┐
Ветер свалил деревья. (Он), ветер, свалил деревья.
└─subj─┘ │ └──obj─┘ └───subj────┘
│ ▲
└────────┘
then the second:
where is
subject? SVA SVA
?? ────────◄─►──┐ ┌──◄─►─────────┐
Ветром свалило деревья. (Оно) ветром свалило деревья.
│ └──obj──┘ │
│ ▲ │
└────────┘ virtual
subj
╒═══════════════════════╕
omission of personal
pronoun, but only `Оно`
does apply here.
╘═══════════════════════╛
We cannot go into the inquiry whether here Оно belong to mystics or metaphisics, but semantically, and this is allowed by grammar, there is always be a virtual subject. Let us be "unphilosophical" but practical, it just work.
And finally, there is a vivid difference in terms of process.
(Оно) ветром свалило деревья.
└──┬──┘ └───┬──┘ └───┬───┘ └───┬───┘
│ instrument │ object
subject process
Ветер свалил деревья.
└──┬──┘ └───┬──┘ └───┬──┘
subject process object
It is worth looking at Vasil's answer, the direction it gives could be used as an additional explanation of the meanings.
Деревья свалило ветром
It is unmarked, default variant without emphasis or with emphasis on ветром.
Деревья свалил ветер
This is most likely used to empathise ветер, otherwise it sounds awkward.
You use impersonal forms when the agent of the sentence is also the instrument (see thematic relations in grammar).
A couple of corpus entries:
Ирину обдало жаром
Помпеи засыпало пеплом
Голову стянуло обручем
Each of those sentences can be rephrased two ways:
Жар обдал Ирину / Печь обдала Ирину жаром
Пепел засыпал Помпеи / Везувий засыпал Помпеи пеплом
Обруч стянул голову / Кто-то стянул голову обручем
, the first sentence using the agent as the subject, the second one using an implied agent and the instrument as the object.
When those conditions are met, the impersonal form is the preferred one.
There are several idioms like ударило током, пахнуло гарью which cannot be rephrased using active voice.
Others, like those above, could be, but this would emphasize the agent's role as an established topic in the conversation:
Везувий выбросил тучу пепла. Пепел засыпал Помпеи.
Impersonal sentences ALWAYS express elemental, unconscious, passive nature of action or state. Second sentence can be transformed into personal one in form:
Деревья были свалены ветром.
Literally:
Trees are felled by wind.
Meaning of impersonal sentence is just same as of passive form. In most cases impersonal sentences should be translated as passive.
Меня сбило с ног.
I was knocked down. \\ I've been thrown off my feet.
One may argue that one should use повалило and повалены as more appropriate verb that have only that exact meaning, without being homophonic to a form of verb свалять (roll up, knead). In real life cases, the verb повалить, translated to English with relatively rarely used verb to fell (not to be confused with past tense of to fall), is actually more frequently used in this situation.
Apart from being neutral and/or emphasising the subconsciopus perception, the words with neutrum verbs (another type of quasi-ergative structure in Russian) work as sentences with dummy pronouns in European languages (French, English and German) except that the dummy pronoun is elliptical (non-evidential).
The structure emphasises the active nature of non-living agent (placed apart from the context and/or rhema of the saying) and it can be both reflexive and non-reflexive verbs:
Светало.
Прояснилось.
Perfective verbs from participles, while non-perfective verbs are more likely to from quasi-ergative structures with neutrum verbs, but this is not mandatory:
Решено. vs Решилось. (both derive from a perfective verb)
Прояснено / Разъяснено. vs Прояснилось. (imperfective VS perfective)
Most of 'elliptical quasi-ergative structures' work both in Present and Past tenses, where the Present Tense is rendered through the Past Passive Participle of archaic type:
Глаза заволошены / заволокло дымкой.
Горло стянуто / стянуло сухостью.
Грудь сдавлена / сдавило тяжестью.
Пламя окутано / окутало тьмой.
Небо озарено / озарило луной.
Горизонт освещен / осветило багровым закатом.
Ночь разлита / разлило невидимой рукой.
Ум охвачен / охватило прозрачностью.
Therefore, the difference is that:
Деревья свалил ветер => The sentence describes evidential cause / state.
Деревья свалило ветром => The sentence descrives non-evidential cause / state.
Thanks to Fenno-Ugric languages.
