No, nominative. "Das" and "Apfel" are the same thing, the subject.

Thanks. I had the same question.

Danke!

Das ist nicht ein Apfel: That is not an apple

Das ist kein Apfel: That is no apple

There's not really a difference between kein/keine and nicht You use kein or keine depending on what gender the word has, where is it uses in a sentence and if it is plural or not

Man:

kein Mann - no man

keines Mannes - of no man

zu keinem Mann - to no man

durch keinen Mann - by no man

Woman:

keine Frau - no woman

keiner Frau - of no woman

zu keiner Frau - to no woman

durch keine Frau - by no woman

Child:

kein Kind - no child

keines Kindes - of no child

zu keinem Kind - to no child

durch kein Kind - by no child

Children:

keine Kinder - no children

keiner Kinder - of no children

zu keinen Kindern - to no children

durch keine Kinder - by no children

You wouldn't.

"apple" in "apple juice" works kind of like an adjective (what kind of juice? apple juice), but German uses a compound noun Apfelsaft that you can't extract the first part out of to use like an adjective.

Nicht negates the verb and kein negates the noun. Kein is sort of like a negative article. K+ein. Not a.

kein is not an, whereas nicht means not. For example, if you put Das ist nicht Apfel, that would be incorrect as you're saying that is not apple, however, if you put Das ist kein Apfel, you are saying that is not an apple which is correct. A little difficult to explain, so ask if you have more questions please! :) It gives us both a learning opportunity.

I wrote "It is not an apple" and Duolingo didn't accept it. Am I right that this is an error?

It is in the masculine nominative. K + ein (masculine nominative article) = kein. Keiner is either the feminine genitive or dative (k + einer)

Kein is used for masculine and neuter nouns, keine for feminine. Das ist kein Apfel (masculine), das ist keine Zeitung (feminine), das ist kein Buch (neuter).

In English, "no" precedes a noun that has no article:

• There is no reason for you to quit your job.
• There are no apples in the basket.

"Not" precedes a noun that has an article:

• That is not a reason to quit your job.
• That is not the reason that I quit my job.
• That is not an apple.

Because you need an article in your sentence.

Because 'Das' and 'Apfel' are the same thing, the subject (sorry, I don't know the correct terms, but that is how I remember it). In your second sentence, 'wir' is the subject and 'Wein' is the object, therefore Wein is accusative. Hope that makes sense.

I believe it is the gender of the noun.

I'm not 100% sure, but in general I've been thinking of 'nicht' as being like 'not' and 'kein' as being like 'no'.

So, "Das ist kein Apfel," is like, "That is no apple."

What you put is not good English, you need an article. You should have said 'this is not an apple', or as Duolingo said, quite rightly, 'this is no apple'.

kein is not an, whereas nicht means not. For example, if you put Das ist nicht Apfel, that would be incorrect as you're saying that is not apple, however, if you put Das ist kein Apfel, you are saying that is not an apple which is correct. A little difficult to explain, so ask if you have more questions please! :) It gives us both a learning opportunity.

Apfel is indeed masculine, but keinen Apfel is the accusative case.

You need the nominative case after the linking verb "to be" (and with a handful of other verbs such as werden "to become").

durch requires the accusative case.

sein "to be" (almost always) has the nominative case on the left and the right.

"This is no apple" is perfectly good English (I am a native English speaker). "This is not apple" is not good English. The correct phrase would be "this is not an apple".