"Он хочет обедать только картошкой."

Translation: He wants to eat only potatoes for lunch.

[plonter99]

Could someone explain why the instrumental is used here?

[2E3S]

Картошка is an instrument of his обед. =)
Обедать is not an action of eating, so we don't use Accusative here like кушать картошку. The literal translation would be "he wants to have lunch with/by (?) potatoes" and not "to have lunch potatoes", maybe this way it would be easier for you to remember.

[Araucoforever]

2E3S, thank you very much for your explanation. I would have never understood the use of the instrumental case in this sentence

[Jordgnoebe]

Bettyru2 posed a sensible follow-up question: should one also use the instrumental case when having other meals? завтракать, ужинать..

[Mel_italian]

Thanks for this explanation 2E3S

[Marc639442]

толко (с) карточкой; C (with) is implicit

[Andrew37421]

"Have potatoes for lunch" marked as incorrect. Обедать - as "have lunch?" Is that not correct? I chose have lunch because the word for "eat" was not present and deliberately left it out.

[Stephen_USA]

"He wants to only eat potatoes for lunch." is rejected. As a native English speaker, I can't see how that's different enough from, "He wants to eat only potatoes for lunch." Just because, "only," usually follows the verb, doesn't mean it's incorrect to precede it. Reporting 14 Oct '21

[Monica129025]

He wants to have lunch with only potatoes. Was my translation. Reported.

[VikPRINCiplE]

только картолькой??))

[Dimitrie_Grinwis]

Only potatoes. Sliced in long narrow strips and deep fried. With a little ketchup.

[jtaylor162]

"He wants to have just potatoes for lunch" is rejected, changing "just" to "only." Reported.

[Peterpurple]

Normally, not always, 'just/ only' come after the subject of an English sentence.

[Miami_14]

From my understanding, the reason there is no "C" here is because the phrase doesn't refer to two things combined (c) e.g. "рис с молоком" but to an accessory/tool/instrument to another thing.
The second ones still imply "with" but there is no need to write the preposition (c). Just the person, the verb and the instrumental case.

[Bolokelen]

'He just wants potatoes for lunch - not accepted.

[Alex630043]

Это старое литературное выражение. Мы, русские, так не говорим.

[soobee620]

Я рада это слышать. Я долго изучала русский, даже преподавала, и жила там несколько месяцев, и я никогда не слышала такое выражение.

[Linus422852]

Uncultured swine...when there are so many different things to eat.

[Tasha706922]

Перевод с английского означает: Он хочет есть только картошку на обед

[Nadin-317]

Зачем так замудрили?
"Он хочет есть только картошку на обед".- лучший дословный перевод.

[PalitoMemito]

Why "he wants to lunch only potatoes" is wrong? Is it something unatural for native english speakers?