The first meaning of the preposition на is “on.” In this meaning it is complemented by the prepositional case.

One interesting and very common use of unchanging это is to refer to a situation broadly. Consider this sentence:

Although «Это были наши соседи» and “It was our neighbors” resemble each other superficially, they are grammatically quite different. In the English sentence “it” is the subject, singular “was” agrees with “it”, and “neighbors” is a predicate noun in the plural. In the Russian sentence соседи is the subject and induces verbal agreement. Notice that это does not agree in gender with anything in the sentence that precedes it. It's not referring to the night. It's not referring to the noise or the neighbors. It refers to the whole, abstract situation. Here are a couple other examples.

This use of unchanging это is not limited to “be” sentences. For instance, in Crime and Punishment Raskolnikov confesses with this phrase:

This use is a bit different than the one we discussed earlier because instead of referring to a whole abstract situation, это serves to direct the listener's focus on the identity of one particular person in the situation:

¹ The precise quote is «Это я убил тогда старуху-чиновницу и сестру ее Лизавету топором и ограбил.» “It was I who killed the old woman and her sister Elizabeth with an axe and robbed them.”

The number of native Russian words that start with э is very small. In that sense it is one of the most uncommon letters in Russian… except for the fact that it is the first letter of это, and это is one of the most common words in Russian. Weird, eh? Something similar is true in English. The number of English words that start with the sound [ð] is very small, but it is the first sound in the English word the, which is among the most common English words. That's really got nothing to do with today's topic, but I've always wanted to say it.

One of the little difficulties for us foreigners studying Russian is to figure out when we need to change это to agree with a noun, and when not. It's confusing because really there are two different это words in Russian. The first we will call “unchanging это,” which has only one form, and the other we will call “adjectival это,” which has endings that change for case, number, and gender. The neuter singular form of adjectival это is spelled the same as unchanging это, and that's where the confusion lies.

Unchanging это is first of all used in the phrase «Что это?», which can be translated quite a few ways, depending on the number of things the questioner is asking about:

Likewise in the response to those questions, это can be translated quite a few ways:

Thus unchanging это can be translated as this, that, these, or those, depending on context. Now notice that in the English translations of those sentences above, whenever we are dealing with unchanging это, the this/that/these/those in English is separated from the noun it refers to by a form of the verb “to be.” That's going to be our rule of thumb for identifying unchanging это:

Rule of thumb: When “this” (or that/these/those) is separated from its noun by a form of “to be,” use unchanging это in Russian.

Unchanging это also appears in какой and чей questions. Here there is a quirk in Russian word order. For instance, an American might expect the translation of “What kind of car is that?” to be «Какая машина это?», where какая agrees with машина in gender and number, and where we use unchanging это because “that” is separated from машина by “is.” That's true as far as it goes. But for some reason the Russians always like to move the это to a position immediately after the question word:

As to adjectival это, it has the following forms:

We use adjectival это to directly modify a noun. When translating adjectival это, there is no form of the verb “to be” between this-these and its noun:

Adjectival это is also used in phrases equivalent to colloquial English “this one” and “these ones”:

Unchanging это has one more quirk. We'll address it in a day or two.

Now here's where the preposition через gets really, really interesting. Observe the following interaction and its translation. The context is a conversation that occurs in a subway car between two subway stops.

Despite the fact that the original contains the word одну “one,” and the translation contains the word “second,” the translation is not an error. The word через means “through,” so the idea is that you need to ride through the upcoming station and get off at the one that follows. Here's another example. The context is two acquaintances standing in front of a building.

«Через два дома», translated word for word, means “through two buildings.” Here the idea is that it's not the building in front of you where Alexandra lives. You need to pass by two buildings, and then you will find the right one. Not that first building, not the second one, but the one after that. And the most concise way to say that in English is with the phrase “the third building.”

This is one of those places where we see that not all languages say things the same way. If you want an English translation of this construction that is concise and sounds natural, then you have to add one to the number that was used in the Russian sentence.

I want to impress upon you how important this concept is. People with no foreign language experience, or language experience only in closely related languages, will assume things like, “If it says ‘five’ in the original, and it doesn't say ‘five’ in the translation, then the translation is wrong.” They may be mistaken. Sometimes a target language simply says things in a different way than the source language, even in such ways that require a change of numbers in the target language.

Let me summarize: if a source text does not correspond word for word with its translation into another language, that does not necessarily mean that the translation is wrong. This may even apply to sentences that contain words that at first glance seem to have an unchangeable meaning (like numbers). Sometimes the little functional words that coordinate everything else throw a wrench into the system and have to be taken into consideration.

Here's where the preposition через starts to get interesting. It can be used in the context where in English we use the phrase “every other”:

In this sense you can often say the same thing in Russian with a paraphrase starting with forms of the adjective каждый every: