First of all, salve itself is the imperative form of the verb 'salvere' - to be well. So it follows the rules for an imperative form, which means that 'salve' is said to a single person, while 'salvete' is said to two or more. The same goes for the farewell, 'vale' - 'vale' is for the singular, and 'valete' is for two or more. :)
Volgav vitsenanieff nivya kevach varatsach.
Yes, there are several different ones. This classical pronunciation reconstruction seems fairly new, and honestly, it makes me cringe. (But then that's not how I learned it. And even though I pretty much forgot everything the pronunciation stuck.)
This page has some Audio examples towards the bottom. https://www.omniglot.com/writing/latin2.htm
It has long been an established fact that the sound of the Latin 'v' of the Classical era is the English 'w' sound. This fact is attested to by the writings of Latin grammarians during this period who describe the way the letter is pronounced. The changes that resulted in the pronunciation of 'v' in modern Romance languages occurred in Latin from around the first and second century CE. See W. Sidney Allen, Vox Latina (Cambridge, 1978) pp. 40-42 and E.H Sturtevant, The Pronunciation of Greek and Latin (Chicago, 1920) pp.38-39 for linguistic discussions of the pronunciation of this letter.
Thank you, I'm sure you must be very lingo-learned, but please have mercy. I don't understand your explanation, and yet I can see that you have the answer so I'm frustrated. I did not take a foreign language at university. Most of those classifications, i.e. "For 1st declension nouns the vocative ending is the same as the nomitive." leave me feeling really stupid. I don't know "declension", "vocative", or "nomative." I surely couldn't determine if a declension were first or second. If there is a way you could pass on your knowledge more simply I would be most grateful. I feel like you should come with subtitles. I do really admire your knowledge of the subject but I wish I understood what you're trying to tell me. Thanks for trying.
This is a big subject but let's see if I can shed some light on it for you.
The first thing to be aware of is that Latin is an inflected language, that is to say the endings of words change to indicate how they fit into a sentence. Words fall into different categories known as parts of speech. This seems to be universal for all languages including of course both English and Latin. The part of speech we are concerned with here is nouns. Nouns are words that stand for things either real or imaginary. So "table" is a noun, and so is "idea". You can't see or touch an idea but as far as grammar is concerned it's just as much a thing as a table is.
Specific names given to people, animals, places and other things are also nouns and they are known as proper nouns. So "Livia" and "Corinna" are both proper nouns. They're also people of course but the words themselves, Livia and Corinna, are nouns. I can say, "the woman is beautiful," or "Corinna is beautiful." The words "woman" and "Corinna" function in exactly the same way in the two sentences, and both are nouns.
Now in English, nouns generally have just two forms: singular and plural. If we say, "Corinna is a beautiful woman," we are using both our example nouns in their singular form. But we might know two people both called Corinna. Then we could say, "The two women over there are the Corinnas." This time we're using our example nouns in the plural.
With Latin the situation is a bit more complex. Latin nouns can still be singular or plural but within those categories they have other forms too. These different forms are known as cases, and these cases are: nominative, genitive, dative, accusative, ablative and vocative. Additionally all nouns belong to one of three genders: masculine, feminine or neuter. So any particular form of a noun can be identified by number, case and gender.
The above is quite a lot to take in but there's a bit more to come. When we look in detail at the way Latin nouns change by case and number they fall naturally into five groups. These groups are known as declensions, and rather unimaginatively they have the names 1st declension, 2nd declension and so on. You can find tables of the case endings of the five declensions here. There's a footnote at the bottom about the vocative. It's not included in the tables as it's usually the same as the nominative. It's only in 2nd declension nouns ending in -us or -ius that it changes.
In the tables you'll see that some of the vowels are shown with a bar over the top. This bar is known as a macron and it's used to indicate when the vowels are long. The Duolingo course doesn't bother with vowel length but if you want to go beyond this course and study Latin seriously, vowel length becomes very important, particulary in poetry.
As to when these cases are used, there's a page on that here. Note that this mentions a seventh case, the locative. This only exists in names of towns, small islands, and a very small number of other nouns. The locative takes the same form as the genitive in the 1st and 2nd declensions, and the same as the ablative in the 3rd declension.
There's a huge amount here and it's quite technical so try not to be intimidated, and give yourself a few days to read it through several times and digest it. If anything is still unclear after that please post again and I or someone else will try to explain further. If you can learn the nouns-declensions table by heart you will be a total star. It's a big challenge but it will really pay off in the long run.
Not just the accent which is actually forgivable, we all have our own accents, but there are many outright errors in the voice samples. Luke Ranieri's (Polymathy's) spoken Latin is superb. If you listen to Luke conversing with Latinists from various parts of the world you will hear their different accents, but they all use the correct restored classical pronunciation.