Questions & Answers about Ο καπετάνιος ελέγχει τον χάρτη.
Because Greek articles change form depending on the gender, number, and case of the noun.
- Ο καπετάνιος = the captain → masculine singular nominative (subject form)
- τον χάρτη = the map → masculine singular accusative (direct object form)
So English uses the for both, but Greek uses different forms.
The article tells you.
- ο καπετάνιος is in the nominative, which usually marks the subject
- τον χάρτη is in the accusative, which usually marks the direct object
So even if you did not know the meaning, the grammar shows that the captain is doing the action and the map receives the action.