"We do not have a dog."
Translation:Wir haben keinen Hund.
Just like when we would say "We have a dog" as "Wir haben einen Hund" and not "Wir haben ein Hund". The masculine articles “der”, “ein” and "kein" change when used in the accusative. “Der” turns into “den” , “ein” into “einen” and "kein" changes to "keinen" . Feminine articles (“die”, “eine” and "keine") and neuter articles (“das” “ein” and "kein" ) don't change. And since Hund (dog) is masculine and is used in an accusative sentence, "kein" will change to "keinen".
All these mean ONE in different genders: masc. neut. fem.
(for the NEGATIVE just add a K at the begining) Here are all the cases....<pre>
DER DAS DIE</pre>
Nominativ ein ein eine
Akkusativ einen ein eine
Dativ einem einem einer
Genitiv eines eines einer
They do not have plurals!!!!! This is all what you need to know!
The declination of "kein, keine, keinen" does not only depend on the gender of the object but also refers to the case. In your example the case of the objects are different. It is "Wir haben KEINEN Hund" because the verb "haben" requires an object in the accusative case and "Das ist KEIN Stern" because "ist" (inf. sein) requires the nominative case.
Funny this sentences theoretically exists in German but it's rarely used in spoken German and not at all in written form - so better don't use it. The connotation is completely different and bit sarcastic "Wir haben nicht einen Hund" is overtly emphasizing the fact that you do not have a dog (i do not own a dog, not even one).
perhaps this little rule can help:
The negation of a nomen with a definite article (der, die, das) is "nicht"
The negation of a nomen with a indefinite article (ein, eine) is "kein, (keiner, keine")
Habt ihr einen Hund? Nein, wir haben keinen Hund.
I hope that helps
best regards Angel
'Keine' and 'keinen' are the negative of 'eine' and 'einen'. Read the following article on 'Ein/Eine/Einen', and hopefully it will explain.
https://www.duolingo.com/comment/871465/Ein-Eine-Ein For a negative statement, simply change 'ein' to 'kein', 'eine' to 'keine' and 'einen' to 'keinen'. Hope it helps!
"accusative" is not a tense, it is a case. Sentences don't have cases, nouns have them. The case determines hich position the noun phrase takes in a sentence. "accusative" marks the direct object. And that's what "a dog" is here, so "a dog" must be in accusative case, which is "einen Hund".