It's not a plural form, it's a genitive case. Russian nouns have several case forms, «сестра́» and «ма́льчик» are Nominative singular forms.
Nominative case forms are used for subjects of the sentences: «Ма́льчик большо́й» (the boy is big), «сестра́ у́мная» (the sister is clever).
«Сестры́» and «ма́льчика» are Genitive singular noun. Genitive nouns have a number of uses. First, it's used in a construction «нет» + Genitive noun to express absence of something (нет ма́льчика 'there is no boy'). Second, it's used after the preposition «у» 'by, at, with'.
By the way, «сестры́» cannot be understood as a plural. Plural would be «сёстры».
My only confusion is that in the audio it sounded like it said сёстры instead of сестры, i dont know if this is just because of accents, or different dialects, or due to stress changing though the last seems the least likely, or if it is possibly and error in the audio.
But that's the Russian. The sentence that conveys the same meaning in English would more usually be constructed with the plural. 'He has no sister.' is not an impossible sentence in English but it is not neutral - it's an odd emphasis (did someone just claim to have met his sister?). We are more likely to say 'he has no sisters [but he has a brother],' or 'He doesn't have any sisters,' in everyday conversation and to me those seem to be the natural translation. We don't insist on 'until we see each other again' for da svidaniya or au revoir.
Actually, to convey this meaning, I would normally use a plural form in Russian too. :D Singular would work in some context when, for example, we spoke about someone having one sister before.
So it's meant to be a weird sentence? This is where Duolingo gets the pedagogy terribly wrong, because aspencer and I were left with the impression that this was being treated as the normal way to express this idea in Russian. And there is no explanation of the intended sense. It doesn't work.
I disagree. "He has no sisters" sounds unusual to me, while answering a question or replying to a statement (perhaps of assumption) about a boy's sister: "why doesn't he ask his sister for help?" I would say something like "he cant, because he doesn't have a sister". I don't think that's specific to New Zealand/ British English either.
That is true, but consider the following situation, in which one party has knowledge of the boy's family where the other does not: "Superintendent, the girl claims to be the boy's sister, she is quite insistent." "Constable, the boy does not have a sister. The girl is an impostor."
Did you report it? Perhaps we should ask if they could put the stress symbol to differentiate them as the stress is in different places on those? It is the reason that I don't like to use the transliterations for languages as often there is not a real letter for a sound and we end up having to learn what they mean anyway, which time could be spent learning the true alphabet.
The microphone exercise has a bug: While the whole sentence is pronounced correctly, the word сестры alone is pronounced as сёстры.
I'm writing here because the in-question reporting system only allows me to report that "The audio does not sound correct", which may prompt staff to only check the whole sentence and find no problem.
Сестры́ (stress on the 2nd syllable) is a genitive singular form of сестра́, roughly similar to 'of sister'. It's also the form we use with «нет» to express absence (У неё не́т сестры́ 'she has no sister'), and the form we use with «у» to express a possessor (У сестры́ есть компью́тер 'the sister has a computer')
Сёстры is the plural nominative form of сестра́, 'sisters'. It's used for the subject of the sentence (Мои́ сёстры мне помога́ли 'my sister helped me') and in the 'X is Y' sentences for both X and Y (Они сёстры 'they are sisters').
There's also се́стры (stress on the 1st syllable), a Church Slavonic doublet of сёстры. It is basically also a nominative plural form of сестра́, but with an ecclesiastical flavour. It could be heard in the church address «бра́тья и се́стры» 'brothers and sisters', and probably in other church-related contexts. It's probably outside of this course's scope.
When spelled without stress marks and without dots over ё, «сестры» can stand for either сестры́, сёстры and се́стры. You'd need to choose the correct form based on the context.
We don't normally write the stress marks.
In very few cases we can write them when the pronounciation can't be guessed from the context (e.g. when you mean бо́льших 'larger' [pl.] and not больши́х 'large'; when there is a strange stress shift in poetry) and in the dictionaries.
I try to mark pronounciation in Duolingo, but I don't do it elsewhere: it would look pretty strange.
You can check it on forvo site https://forvo.com/word/%D1%81%D0%B5%D1%81%D1%82%D1%80%D1%8B/#ru
On PC desktops and laptops, you can add languages and a variety of keyboards under Windows. I added the American English - International keyboard and deleted the standard keyboard which enables me to type in English, Spanish, Italian, and French, and probably Portuguese (I don't know about that, though). I added Russian language and the Russian Mnemonic keyboard, so I can type Cyrillic. I use the Windows Key-Space Bar to shift between keyboards. For a few characters, like « » œ — ¡ and ¿ I use Alt-Code.
This sentence should be pronounced сестры́, the genitive-case singular form of сестра́. (After нет, we use genitive case.)
Other pronunciations don’t work here. Сёстры ‘sisters’ is a nominative-case plural of сестра́ (another option is се́стры, an alternative old-fashioned variant of сёстры used in Church, and it’s even less likely). You can’t use nominative after нет.
Why does the voice (in the listening exercises) always pronounce genitive singular of "сестра" with accent on the first syllable??? In almost every exercise about "not have"!!! "Нет сёстры" is wrong. I reported this bug again and again. It seems to me that no one of the DL team read it.
This is a bug.
Russian has a letter ё (yo). It's not uncommon to drop dots over ё, so сёстры becomes undistinguishable from сестры́.
In Duolingo, Cyrillic script distinguishes between сестры́ (genitive of 'sister') and сёстры (plural nominative, 'sisters'), but Latin script renders both sestry. So, the exercise is doable in Cyrillic script, but impossible in Latin.
Fortunately, there aren't many such bugs, so you won't see this often.
But I'd recommend learning Cyrillic script and doing Duolingo in Cyrillic. It might look complex, but it just has 33 letters. Russian is rarely written in Latin script (you probably won't see it outside of Duolingo and SMS messages), so learning Cyrillic will allow you to read unadapted texts.
I'm from the US and use Windows 10. I type in Cyrillic on Duo for the Russian course. There's no button to push, although I vaguely recall a choice between seeing Duo's Russian-language exercises in Cyrillic or the Western alphabet. I loaded Russian language into Windows 10, then loaded the Russian Mnemonic keyboard. There is also a standard Russian keyboard, which would be useful for native-speaking Russian touch-typists.
Here's an article I wrote about this topic:
Windows 10 Russian Mnemonic Keyboard
I suggest that English speakers use the Russian Mnemonic keyboard. Identical letters such as a, e, m, and o occupy the same keys in both languages. Russian equivalent letters with characters which differ from their Engish counterparts in form but not function occupy the English letter equivalent to the Russian character: the Russian “i” = “и” is entered in Russian text by pressing the “i” key on your keyboard. Similarly, the Russian “r” = “р” is entered by pressing the “r” on the keyboard. [This text is being written using [Windows key + SpaceBar] to move easily back and forth between keyboards.]
Some Russian letters have no direct English equivalent, and must simply be learned. Pressing English “x”, for example, produces Russian “ж” and English “w” produces Russian “ш”.
In order to enable the Russian Mnemonic keyboard, first you will have to load the Russian language module in Control Panel/Languages/add a language. When the Module is loaded, return to Control Panel/Languages/ Русский and click on options. Inside options, click on add an input device. From the list of keyboards that appears, select Russian – Mnemonic, then click on “add”. When you are returned to the list of languages, click on “save”, then exit Control Panel.
You can switch among keyboards by pressing the Windows button and Space-bar. You also find a keyboard-selection button on the taskbar. In using the Mnemonic keyboard, some Russian letters and pronunciation marks do not appear immediately when the key is pressed, but require the pressing of an additional key or the spacebar in order to appear. You will have to do some trial-and-error to figure this out.
Some Russian characters require the pressing of two keys in quick succession, such as “ju” or "yu" to get “ю”.
In using the following chart, you switch to the Windows 10 Russian Mnemonic keyboard using the Win + Space-bar combination or selecting the Russian Keyboard from the task-bar. You press the key(s) listed under the English Keyboard header to get the Russian letter under the Русский Алфабит (Russian Alphabet)
Русский Алфавит = English Keyboard
а А = a A
е Е = e E
к К = k K
м М = m M
о О = o O
т Т = t T
Русский Алфавит = English Keyboard
б Б = b B
д Д = d D
ф Ф = f F
г Г = g G
л Л = l L
и И = i I
н Н = n N
п П = p P
р Р = r R
с С = s S
у У = u U
в В = v V
з З = z Z
Other Russian Letters
Русский Алфавит = English Keyboard
ы Ы = y Y + Space-bar
ц Ц = c C + Space-bar
х Х = h H
й Й = j J + Space-bar
ш Ш = w W
ж Ж = x X
я Я = q Q or ja JA
щ Щ = sc SC
ч Ч = ch CH
ё Ё = jo JO or yo YO
э Э = je JE or ye YE
ю Ю = ju JU or yu YU
Russian Pronunciation “letters”
Русский Алфавит = English Keyboard**
ь Ь = ’ ”
ъ Ъ = ` ~
«Russian Quotation Marks»
Русский Алфавит = English Keyboard**
To enter Russian quotation marks using a PC keyboard, you have to use the Alt Key method: Hold down the Alt and enter a four-digit code using the numeric keypad, then release the Alt key, and the special character appears. The four numbers (including 0 = zero) are “Unicode” numbers which translate according to a universal table of symbols developed by Microsoft.
— = Alt+0151
« = Alt+0171 (Left Angle Quote)
» = Alt+0187 (Right Angle Quote)
All the Russian characters could be entered this way, using different numbers, but why bother when you can use the Russian keyboards available from Microsoft. Some other symbols:
¡ = Alt+0161
¿ = Alt+0191
æ = Alt+0230
œ = Alt+0156
ª = Alt+0170 (Feminine Ordinal) º = Alt+0186 (Masculine Ordinal)
€ = Alt+0128
£ = Alt+0163
© = Alt+0169
® = Alt+0174
÷ = Alt+0247
§ = Alt+0167
Do not try to use the Windows virtual keyboard, because that is missing a number of Russian letters.
It is common (and usually considered ok) for Russians to not write ё at all, instead writing always е for both е and ё. This is due to historical reasons (ё is a very modern letter compared to the other Russian letters, and appeared in order to explicitly write a "pronunciation shift" that occurred over the centuries in some words where there was previously a е sound).
In this course and in learner's/children material in general, ё is always written explicitly so that you can learn. However, probably due to this ё/е thing, the text-to-speech software gets it wrong many times. In this sentence, it is сестры, the genitive singular. The audio is plain wrong because it is getting confused with сёстры (which is spelled the same if you write everything with е). You can check all the forms in wiktionary: https://en.wiktionary.org/wiki/%D1%81%D0%B5%D1%81%D1%82%D1%80%D0%B0