"He has a calendar."

Translation: Αυτός έχει ημερολόγιο.

[Nicolas550181]

Still no explanation why the article ένα is left out.

[H.Melissopoulos]

"Αυτός έχει ημερολόγιο" was accepted, it is correct to omit ένα?

[D_..]

Yes, it is correct!

[Frogfall]

Why is it correct to omit ένα?

[PeterBrouwer1]

Why is έναν ημερολόγιο incorrect?

[troll1995]

Because ημερολόγιο is a neuter noun, so the indefinite article is ένα and not έναν which is the indefinite article for masculine nouns. ;)

[PeterBrouwer1]

Thanks, clear!

[MarkHamilt980350]

Can anybody point me to a good resource that explains clearly when articles can be omitted and when they are required? All I can find, either in the discussion forums, or through on-line resources is statements like: "The indefinite article can most often be omitted." That's really not all that helpful.

[troll1995]

As a rule of thumb, you can omit the indefinite article when the noun can't be more than one. Είμαι άντρας=I am a man (I can't be two men), but είδα έναν σκύλο=I saw a dog (because it could have been two dogs). :)

[MarkHamilt980350]

Thanks. Every little bit of knowledge helps.

[LeonAchill]

But you can have more than one calendar... I don't get it.

[G.Georgopoulos]

It sounds better if the article is included, but if the discussion calls for a yes/no answer about whether somebody possesses a calendar, then the article is unnecessary. Bear in mind that this best works for questions.