Modifiers of the noun
Apposition, attribute, genitive: how one noun narrows another — in the same case or a different one.
Same case: apposition
The second noun matches the first one’s case: ο φίλος μου ο Νίκος (my friend Nikos); in the genitive both members decline together: του φίλου μου του Νίκου.
Different case: the genitive attribute
The genitive expresses belonging, material, content, quality: το κλειδί του σπιτιού, άνθρωπος μεγάλης καρδιάς (a person of great heart). Note the contrast: ποτήρι κρασιού (a wine glass) / ποτήρι κρασί (a glass of wine — accusative!).
The attribute and its article doubling
The adjective sits between article and noun: ο ψηλός άντρας. Doubling the article — ο άντρας ο ψηλός — singles out and stresses. After the noun WITHOUT an article the adjective turns predicative: Ο άντρας είναι ψηλός is a sentence, no longer a noun phrase.
Your turn
Choose the correct form.