Když překládám množné číslo "knihy" - nemusím předsouvat člen THE x A ? Děkuji.
"The" je jak v množném, tak v jednotném čísle. Ovšem člen "a/an" je jen v jednotném čísle a v množném se vynechává.
Takže tady jsou správně obě varianty: "I read the books" - "Čtu ty knihy (co jsme se o nich už bavili)" vs "I read books" - "Čtu (nějaké) kníhy" či "Čítávám knihy (jakože to mám ve zvyku)", což je vlastně použití neurčitého členu u podstatného jména "books".
Hezký článek o základech ke členům je tu: http://www.helpforenglish.cz/article/2006072901-cleny-v-anglictine-articles
I have noticed that sometimes y at the end of the word indicates plural (you might remember from a few days ago that I am using this tree to learn Czech. I speak English natively) and sometimes it's i. When do I use each one?
oh. I missed the 'y' in your first question.
This depends on gender of the item being pluralized a lot. Book is a female. There are 4 female representative words that one has to learn and use them as a pattern word (I am sure there is some gramatical word for this but I do not know it, in English anyway). So book, or rather 'kniha' follows the specimen 'žena' (woman).
Plural for žena is ženy and thus for kniha is knihy. (In both cases again you cannot really put an i because both 'n' and 'h' can only be followed by a 'y'. So kind of a double hint. In any case it all boils down to gender.
I'm not sure, it looks that you missed our answers to your question here: https://www.duolingo.com/comment/5159990
As I wrote there - after h has to be always "y" (unles it's a foreign word like "historie")
To the gender thing - maybe our non-native contributor can say more, but it's probably like in German - just memorise it...
You do not. You need to learn it. Though if you do have a word ending in an 'a' you can be nearly sure it is feminine. If it is 'o', you can be nearly sure it is neutral = it. Just like any other language with genders you need to learn them. And not relly on learning that something is feminine in french or german it would be femine in czech or any other language. Even words that sound exactly the same can have different genders. 'Tramvaj" in czech is a she'. Tramvaj (both meaning a tram/street car) in russian is a he....
Even the obvious ones are often not what any normal person would think. "Děvče", one of the standard words for "girl", is neuter, for example.
Hopefully this will be taught in a systematic way when we do the Czech for English course, but it's not something we've had to think about so far in the English for Czech course since Czechs generally just know the genders of Czech words.
For now I would suggest using the link I posted in the earlier discussion: Internet Language Reference Book