Are "домой" and "дома" interchangeable and if not, what's the difference?

Question

During a Duolingo Russian lesson the other day, I translated the following:

"My place is at home,"

with

"Моё место домой,"

but the answer given was:

"Моё место дома."

A Google search seems to indicate that both are legitimate sentences, but my version -- using "домой" instead of "дома" -- does not seem to be used very often. Does anybody know what the differences are between these two versions of this sentence?

Answer 1

I suppose, your confusion stems from the fact, that in English different use cases of "home" can be translated to Russian as either "домой" or "дома". Like in:

• "I'm going home" — "Я иду домой"
• "I'm home (at last)" — "Я дома (наконец-то)"

In Russian "домой" and "дома" are absolutely different words.

The word "домой" means a direction to home and answers to the question "where" in English, but "куда" in Russian, like:

• это дорога домой — this is a road to home
• я иду домой — I'm going home

The word "дома" means a place, location and also answers to the question "where" in English, but "где" in Russian, like:

• я дома — I'm home
• мое место дома — my place is at home

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That is they are not interchangeable and the only correct translation for "My place is at home" is "мое место дома", except a case, where the phrase "my place" means one's home itself, like "do you have a TV at your place". But in that case the phrase "My place is at home" would look very strange in and of itself.

Answer 2

No, they are not interchangeable at all. Домой means "home, homeward" (as in "go home"), and дома means "at home" (as in "stay at home").

Thus, "моё место дома" is indeed correct, because it answers the question "where is my place"? At home.

Now you can just memorize these forms the way they are but at some stage of learning Russian it's just inevitable to need to learn more about Russian cases.

See there are no cases in modern English at all (only some traces like "who"/"whom"/"whose") but you just know what's the difference between "at home", "by home", "to home" etc. - it's just something you've actually memorized - some of information that is passed by prepositions in English is passed by the cases. It's just the way it is.

Well, it's even more tricky, technically, "домой" and "дома" are adverbs, not nouns, so it's not correct to talk of cases but actually those are historically just "frozen" forms of noun дом.

And, to introduce even more confusion, those are "frozen" form of so called smaller cases - one that are not used for all nouns but there are some remnants of ancient, richer than modern, conjugation system.

So, just accept it the way it is ;)