"He has an apple."
Translation:Er hat einen Apfel.
Ein and Eine is for subjects of a sentence, like "An apple is __" or "The book is green.
Ein/eine/einen are for objects, like "I eat AN apple", "I read A book", "I have A newspaper" Ein is for neuter objects, like das Buch, Eine is for feminine objects like die Zeitung, and Einen is for masculine, like der Apfel.
'Ein' is not only for neuter object, but can also serve for nominative of masculine, e.g. 'A man (Ein Mann) is reading'.
'Einen' can only serve for accusative of masculine but not for nominative, e.g. 'A man eats an apple' should be 'Ein (but not Einen) Mann isst einen Apfel'.
Wodanaz's answer includes every situation.
this is incorrect, specifically "Ein is for neuter objects, like das Buch, Eine is for feminine objects like die Zeitung, and Einen is for masculine, like der Apfel.." Ein is masculine. Einen is also masculine but used on the accusative case. see https://www.duolingo.com/skill/de/Accusative-Case/tips-and-notes
For the articles, nominative and accusative are nearly the same. Only the masculine ("der") forms change:
"a(n)" masc. neut. fem. Nominative ein ein eine Accusative einen ein eine
I don't understand you very well; but you shouldn't memorize it for every word; the only thing you must, is the gender for every word. Knowing that, you must identify the grammar case (nominative (nom), accusative (akk), dative (dat) or genitive (gen)), so that you can declene properly. At this point you should worry only for the first two cases.
No. The difference between "a" and "an" is due to pronunciation (it changes when followed by a vowel). German does not care about this. German cares about whether the object is performing an action (the "nominative case") or receiving an action (the "accusative case"), and there are two other cases that I don't understand well enough to explain at this point.
So in German if "apple" is the subject of the sentence it will have "ein" as the article, and if it is the receiving object of a verb, it will have "einen".
Subject: "Ein Apfel fällt vom Baum." (An apple falls from the tree.)
Object: "Ein Junge isst einen Apfel." (A boy eats an apple.)
Because "ein Apfel" is a masculine noun, it changes in these cases. Note from vkmear's comment above that both neuter and feminine nouns would appear not to change in situations like this, because their article in the nominative (aka "subject") and accusative (aka "direct object") cases stay the same -- "ein" for neuter nouns and "eine" for feminine nouns.
It's INCORRECT einen! because the Apfel isn't in Akkusativ !
Indefinite article Masculine: Nominative - ein Accusative - einen Dative - einem Genitive - eines
The accusative case (abbreviated acc) of a noun is the grammatical case used to mark the direct object of a transitive verb. Clearly isn't the case of this example!
In German, as you will learn, there are 4 ‘cases'. To my understanding, these cases try to explain the relationship between the elements of the sentence; between the subject and other subjects (which are called objects - be it person, animal or thing). And the articles (and pronouns) of these objects change depending on the case. Here we have the first two:
Ein Apfel ist rund > Nominative case: Apfel is the subject or the sentence [Subject verb description]
Hans isst einen Apfel > Accusative case: Apfel is the object of the sentence, and Hans is the subject [Subject verb object or secondary subject]
For example, the (indefinite) article for the masculine noun Apfel is EIN in the Nominative case. This is because Apfel is the subject or the main actor in the sentence. It answers the question: What is round? Notice also how ‘Ein Apfel’ comes before the main verb (ist). On the second case, the article for Apfel changes from ein to einEN because Apfel is NOT the subject of the sentence; it is the supporting actor or the object, and because the main actor (Hans) is doing something to it. Again, notice how Apfel comes now after the main verb. But the key here is the verb. It has to indicate that something is being done to the object of the sentence, in this case: the apple.
I am not too clear when some verbs are more Accusative than others, but I can tell you one thing: only masculine nouns make the articles (and pronouns) change - feminine and neuter nouns do not change with the Accusative; this could be one reason for so much confusion. And this is also why is very important that you learn well the gender of German nouns. Hope this helps. :0)