In short

Some Greek verbs never take a personal subject. They sit permanently in the third person singular and either introduce a να-clause (πρέπει να φύγω “I have to leave”), or describe the weather and the world (βρέχει “it is raining”, κάνει κρύο “it is cold”, υπάρχει “there is”). A third group is only half impersonal: with μου αρέσει and με πονάει the thing is the grammatical subject and the person is a weak pronoun — so Greek says “the coffee pleases to-me” and “the head hurts me”. Getting these three patterns right removes a large share of beginner errors, because English builds all of them with a personal subject.

The rule

1. Impersonal modals + να. A small closed set of forms — πρέπει, μπορεί, χρειάζεται, απαγορεύεται, επιτρέπεται, αξίζει, φαίνεται — is frozen in the 3rd person singular and is followed by να + subjunctive. The person doing the action is expressed only by the ending of the verb after να:

Πρέπει να φύγω. — I have to leave. Πρέπει να φύγουμε. — We have to leave.

πρέπει in particular has no first- or second-person forms at all. There is no *πρέπω, no *πρέπεις, no *πρέπουμε. Its past is the equally frozen έπρεπε. Negation goes on the impersonal (δεν πρέπει να = “must not”; δεν χρειάζεται να = “there is no need to”).

2. Personal modals + να. Beside these, Greek has ordinary conjugated verbs that carry modal meaning: μπορώ “I can, I may” and ξέρω “I know (how to)”. These agree with their subject like any verb, and they too are followed by να, never by an infinitive — Greek has none.

Μπορώ να οδηγήσω. — I can drive. Ξέρεις να κολυμπάς; — Can you (do you know how to) swim?

The 3rd singular μπορεί is therefore ambiguous by design: Ο Νίκος μπορεί να έρθει can mean “Nikos is able to come” (personal) or “Nikos may come, perhaps Nikos will come” (impersonal). Only context decides.

3. Weather and existence. Weather verbs have no subject whatsoever — no equivalent of the English dummy “it”. Βρέχει. is a complete, well-formed sentence. Temperature and conditions use κάνει (κάνει κρύο, κάνει ζέστη) or έχει (έχει ήλιο, έχει συννεφιά). Existence uses υπάρχει, which has no dummy subject like the English “there”: the thing that exists is its real subject, and the verb agrees with it — υπάρχει πρόβλημα, but υπάρχουν προβλήματα.

4. Experiencer verbs. Here the English subject becomes a weak pronoun and the English object becomes the Greek subject. Two sub-patterns, distinguished by the case of the clitic:

• Weak genitive: αρέσει, λείπει, φαίνεται, αρκεί, χρειάζεται, συμβαίνει — μου αρέσει ο καφές, σου λείπει η θάλασσα.
• Weak accusative: πονάει, ενδιαφέρει, νοιάζει, πειράζει, ζαλίζει — με πονάει το κεφάλι, δεν με νοιάζει η τιμή.

In both, the verb agrees with the thing, not with the person: μου αρέσει ο καφές but μου αρέσουν τα βιβλία· με πονάει το χέρι but με πονάνε τα πόδια.

Forms & patterns

Impersonal forms (3rd singular only)

πρέπει never conjugates — the person appears after να

Personal modals: μπορώ (B2 conjugation) and ξέρω (A conjugation)

Weather and existence

Experiencer pattern A — weak genitive (αρέσει, λείπει)

Experiencer pattern B — weak accusative (πονάει, ενδιαφέρει)

Examples

Common mistakes

• Πρέπω να φύγω. -> Πρέπει να φύγω. — πρέπει has exactly one form; the person is shown by the verb after να, never by πρέπει itself.
• Πρέπει φύγω. -> Πρέπει να φύγω. — Greek has no infinitive, so να is obligatory after every modal, personal or impersonal.
• Δεν χρειάζομαι να έρθω. -> Δεν χρειάζεται να έρθω. — χρειάζομαι takes a noun (χρειάζομαι βοήθεια); before a να-clause use the impersonal χρειάζεται.
• Είμαι κρύο σήμερα. -> Κάνει κρύο σήμερα. / Κρυώνω. — weather is κάνει κρύο; είμαι + adjective would say what you are, and “I feel cold” is the verb κρυώνω.
• Αρέσω τον καφέ. -> Μου αρέσει ο καφές. — the thing liked is the subject in the nominative; the person is a weak genitive pronoun.
• Μου αρέσει τα βιβλία. -> Μου αρέσουν τα βιβλία. — the verb agrees with the plural thing, not with the person.
• Πονάω το κεφάλι μου. -> Με πονάει το κεφάλι μου. — with πονάει the body part is the subject and the person is a weak accusative pronoun.
• Είναι ένα πρόβλημα. -> Υπάρχει ένα πρόβλημα. — “there is” is υπάρχει, and it becomes υπάρχουν with a plural.

Tips

• Learn πρέπει, χρειάζεται, απαγορεύεται, επιτρέπεται, αξίζει as fixed blocks, like English “one must”: whatever tense they turn up in, they stay in the third person singular — έπρεπε, θα πρέπει, χρειαζόταν, χρειάστηκε.
• μπορεί is two-faced. With a personal subject it means “is able to”; standing alone in front of να it means “maybe” — Μπορεί να κοιμάται. “He may be asleep.”
• Memorise the experiencer verbs in two lists by case: genitive μου αρέσει, μου λείπει, μου φαίνεται· accusative με πονάει, με ενδιαφέρει, με νοιάζει, με πειράζει. There is no rule that predicts which list a verb belongs to.
• Use the plural test to check agreement: if the thing goes plural, so does the verb — αρέσει → αρέσουν, πονάει → πονάνε, υπάρχει → υπάρχουν.
• For contrast or emphasis, add the strong pronoun in front: Εμένα μου αρέσει η θάλασσα, εσένα σου αρέσει το βουνό.
• In speech μου αρέσει regularly elides to μ’ αρέσει, and σου αρέσει to σ’ αρέσει; write the full form in careful prose.
• Weather sentences need no subject at all. Do not translate the English “it”: Βρέχει. Χιονίζει. Νυχτώνει νωρίς τον χειμώνα.