"This is his household."

Translation: Das ist sein Haushalt.

[Daniel535983]

Why can't i use Dies instead of Das?

[az_p]

That should also be correct. I hope you reported it!

It would be used less-often in spoken German, though, as it sounds a bit formal.

[mizinamo]

I've added it now; thanks!

[Asile7223]

Why is "Dieses ist sein Haushalt." incorrect? A brief search turned up https://en.wiktionary.org/wiki/dies#German, which indicates that Dies and Dieses should be interchangeable. Is this not correct?

[mizinamo]

It doesn't feel like it to me, no.

I would use dieses to mean "this one" (i.e. referring to a particular one out of a group of specific nouns you had been discussing) but dies to mean "this" (i.e. referring to something new).

[remludar]

Why not "Das ist seines Haushalt?" Someone said before that possessive pronouns are treated as indefinite articles. That would mean here an ending of -es for Nominative Nuetered no?

[mizinamo]

That would mean here an ending of -es for Nominative Nuetered no?

No. We don't say eines Buch or eines Mädchen either, do we?

It's ein Buch, ein Mädchen, ein Haushalt; mein Buch, unser Mädchen, sein Haushalt. No ending for neuter nominative.

[remludar]

Yes. I was thinking about adjectives instead of indefinite articles. My mistake. Thank you!

[Bill80776]

I am now confused as to why in this sentence it is 'sein' and not 'seiner.' The noun is masculine, the case is nominative, and since there is no definite article then the 'er' signifier is needed. Or have I missed something?

[mizinamo]

The possessive determiners mein, dein, sein, ihr, unser, euer act like the indefinite articles ein, kein in taking no ending for masculine nominative and neuter nominative/accusative.

So for masculine nominative, it's sein, not *seiner (which would be only feminine genitive/dative or plural dative).

Also, you wrote:

since there is no definite article

Firstly, that rule is for adjectives; secondly, the criterion is not "definite article" but rather "determiner that shows an ending for gender/number/case".

Definite articles are just one form of determiner; other possibilities include indefinite article (eine), demonstrative determiners (diese), and possessive determiners (meine).