"The boys like that."
Translation:Is maith leis na buachaillí é sin.
The phrase for liking things is Is maith le ABC XYZ.
ABC is the person who likes something and XYZ is the thing they like.
Is maith le Máire tae. Máire likes tea.
le + an = leis an Is maith leis an chailín an pictiúr. (gcáilín would also be correct.)
le + na = leis na Is maith leis na buachaillí é sin <<< This is what you should have written.
To put it a different way: without the é, sin is modifying "na buachaillí," turning it from "the boys" to "those boys." With the é, "é sin" forms a pair, becoming "that." I think this is a real interesting garden path sentence, since you don't know until you get to that é what the actor in this sentence is.
When you use this expression, the person who is liking something has to come after 'le'
Is maith le XYZ bainne = XYZ likes milk
Is maith liom caife = I like coffee
Is maith leat... = You like...
Is maith leis... = He likes...
Is maith léi... = She likes
Is maith linn... = We like...
Is maith libh... = You like...
Is maith leo... = They like...
Is maith leis an bhean... = The woman likes...
Is maith leis na mná... = The women like ...
Is maith le mo mhac ... = My son likes...
Note that le changes to leis in front of an and na.
I wish Duolingo gave good enough grammar explanations that people like you weren't forced to crowd-source their grammar answers. Daltaí is, at least, better than what you're likely to get on these forums.
The difference is not between leis (which is simply the form of le used before an and na) and le. It is between the initial mutation or lack of it used after an and after na. In your examples, there is an initual mutation after an but not after na. That pretty much sums it up. Mutate after an but not after na. Charts: http://www.nualeargais.ie/gnag/artikel.htm#praeposition
Note that there are two accepted systems of initial mutations after prepositions. I would say ar an bhus and leis an bhó, never ar an mbus or leis an mbó, and I would be right, too. Dunno if Duolingo tells you that.
More than you ever wanted to know about prepositions: http://www.nualeargais.ie/gnag/praepos.htm
Unsolicited advice: Get a grammar book!
I did do Duolingo when it first came out, but I already knew a lot of grammar and quickly became disillusioned because there were a lot of mistakes and because answers in Ulster Irish were marked wrong. I started submitting error reports, and Duolingo changed some questions to accept Ulster answers, and they fixed some of the sentences with mistakes. (No one seems to respond to error reports now.) If you make a comment on a page, DL notifies you whenever there's another comment on the page -- I have no special powers!
I've learned several languages in which I am now fluent. Other than when I studied Vietnamese (briefly), I have never had so much trouble with a language. Ever. I slog along with Irish, year after year, while flying through other languages. Why is this so hard? Am I missing something? I never encountered declension in ANY other language. Does it even exist in other languages?
Sure it does. Russian has big time changes for declensions. English does for pronouns, I/me/mine, etc. French does for pronouns, il/le/lui, etc. German does for pronouns er/ihm/ihn, the definite article der Apfel/den Apfel/dem Apfel/des Apfels, plural nouns in the dative case, masculine and neuter nouns in the genitive case, adjectives and so on. Other Slavic languages decline nouns and modifiers. And then there's Latin!
If you are really 'slog[ging] along with Irish, year after year,' perhaps you should try a different program. I'm serious, and I mean it in the most helpful way possible. After 'year after year,' you should have outgrown Duolingo. Get a real program with adequate audio and good explanations of the grammar. First choice would be a real class (online or in-person) with a real teacher. Next best would be either the Irish classes on FutureLearn (www.futurelearn.com) or the Ulster Irish series Now You're Talking (book pages, sound files, videos, answer key all at ultach.org).
Why spend any more time on a program that isn't working for you?
We're supposed to say The boys like that
the boys = na buachallí
like = Is maith le (person who likes th thing) (thing that is liked)
that = é sin
When you put it all together, you get /is maith le na buachaillí é sin/, but whenever you want to say 'le an' or 'leis an,' STOP and write leis an or leis na. It's just one of those things that every language has, like in English, when you want to say 'a' in front of 'apple' or 'unicorn,' you have to STOP and say 'an' because we just don't say 'a' in front of vowels.
In Is maith leis na buachaillí sin, na buachaillí sin is what is liked.
In Is maith leis na buachaillí é sin, é sin is what is liked.
That's why you need to say é.
Is maith leis na buachaillí sin - https://forum.duolingo.com/comment/4313347
"He like those boys"
Is maith leis na buachaillí é sin - https://forum.duolingo.com/comment/6443468
"The boys like that"