In short

Everyday Greek prepositions take the accusative (σε, από, με, για, χωρίς, πριν από). A second, smaller set — inherited from the learned written tradition — takes the genitive: λόγω, εξαιτίας, μέσω, κατόπιν, χάριν, εντός, εκτός, πλην, άνευ, εναντίον, υπέρ, μεταξύ, προ, εκ/εξ, and the two-faced κατά and περί. Most of them live in notices, contracts, news reports and careful speech, and most have a plain everyday twin you already know. Two do not: μεταξύ and εξαιτίας are ordinary, unmarked words that simply happen to take the genitive (Το συζητήσαμε μεταξύ μας· Δεν ήρθε εξαιτίας της δουλειάς του), and they need no formal surroundings at all.

Two things make them easy to control: the article and the noun after them must both be genitive (λόγω της βροχής, not λόγω η βροχή), and with a pronoun they take the weak genitive clitic (εναντίον μου, υπέρ μας, μεταξύ μας), never a strong pronoun. Four of them — κατά, περί, μετά, υπέρ — change meaning with the case: κατά της απόφασης “against the decision” against κατά την απόφαση “according to the decision”.

The rule

1. They govern the genitive of a full noun phrase. The genitive is not carried by the noun alone: the article, any adjective and the noun all agree. Λόγω του σοβαρού προβλήματος. Εναντίον της νέας απόφασης. If you can say the noun phrase in the nominative (το σοβαρό πρόβλημα), you only have to move it one step — see The genitive case.

2. They take weak genitive clitics for pronouns. Greek has no accusative object of these prepositions, so the pronoun cannot be strong: εναντίον μου (not εναντίον εμένα), υπέρ σου, μεταξύ τους. This is the same weak genitive series you met as the indirect object, and the clitic follows the preposition rather than preceding it.

3. They take noun phrases, not bare clauses. Greek λόγω / εξαιτίας correspond to English “because of” + noun. For “because he was late” you switch to a conjunction: επειδή άργησε. There is no εξαιτίας που, no λόγω ότι: a clause follows them only once the article nominalises it (εξαιτίας του ότι, λόγω του ότι), and that is heavy officialese — επειδή is the better choice. Εκτός is the exception in this set: both εκτός που and εκτός του ότι are normal Greek (εκτός που άργησε, ξέχασε και τα εισιτήρια), and πλην του ότι works the same way.

4. Case can be the meaning. With κατά, περί, μετά and υπέρ, the same word points in two directions and only the case tells you which. Learn them as a pair, not as a word.

5. They are a register, not a default. Most have an everyday equivalent: λόγω ≈ εξαιτίας or an επειδή-clause, άνευ ≈ χωρίς, προ ≈ πριν από, εντός ≈ μέσα σε, εκτός ≈ έξω από / εκτός από, κατόπιν ≈ ύστερα από. Use the learned form when the surrounding sentence is formal, and keep it consistent — a κατόπιν in the middle of chatty speech sounds like a parody of a civil servant. Μεταξύ is outside this game: it is a plain inherited word, so ανάμεσα σε is a synonym rather than a plainer twin — μεταξύ μας, μιλήστε μεταξύ σας, γνωρίζονται μεταξύ τους are everyday speech.

6. εκ becomes εξ before a vowel. Εκ των πραγμάτων, εκ νέου, εκ μέρους μου — but εξ αρχής, εξ ολοκλήρου, εξ αποστάσεως. The compound εξαιτίας is simply εξ + αιτίας welded together. Frozen dative phrases (εν τω μεταξύ, δόξα τω Θεώ) are a different survival and belong to Katharevousa relics and the formal register; compound prepositions built on σε (πάνω σε, μαζί με, εκτός από) belong to Further and compound prepositions.

Forms & patterns

The genitive-governing prepositions with a full noun phrase

The everyday twin

Weak genitive clitics after the preposition (all six persons)

Μεταξύ needs either a plural referent or two terms joined by και (μεταξύ Ελλάδας και Ιταλίας, μεταξύ ζωής και θανάτου, μεταξύ δέκα και είκοσι ευρώ), so only the plural clitics work with it. Some of the others take the same clitics — εξαιτίας σου, εντός μου, εκ μέρους μου — but not all of them: λόγω and χάριν are used only with a noun (λόγω της βροχής, χάριν συντομίας), never *λόγω μου.

One preposition, two cases

Τα υπέρ και τα κατά (“the pros and cons”) shows both words used as nouns; there the case question disappears.

Full paradigms of three nouns you will put after them

Watch the accent: το πρόβλημα → του προβλήματος → των προβλημάτων, and η απόφαση → οι αποφάσεις → των αποφάσεων. In formal writing the learned genitive singular της αποφάσεως is also alive after exactly these prepositions (εξ αποστάσεως, κατόπιν συνεννοήσεως, άνευ αδείας) — that class is Learned noun and adjective classes.

Second accent. When a three-syllable-stressed genitive is followed by a clitic, it takes an extra accent on its final syllable: κατόπιν αιτήματός σας, λόγω του προβλήματός σου, εξαιτίας του μαθήματός μας.

The same words as verb prefixes

Examples

Common mistakes

• λόγω το πρόβλημα -> λόγω του προβλήματος — the whole phrase moves into the genitive, article included.
• λόγω της βροχή -> λόγω της βροχής — the article alone is not enough; the noun takes its genitive ending too.
• εξαιτίας που άργησε -> επειδή άργησε (or εξαιτίας της καθυστέρησής του) — λόγω and εξαιτίας take noun phrases, not clauses (unlike εκτός, which does allow εκτός που).
• λόγω ότι δεν είχαμε χρόνο -> επειδή δεν είχαμε χρόνο — same reason; a bare ότι-clause never follows λόγω, only the officialese λόγω του ότι.
• υπέρ την πρόταση -> υπέρ της πρότασης — with a noun phrase υπέρ governs the genitive. The accusative is not only a fossil (υπέρ το δέον): spoken Greek does say είναι υπέρ μας “it’s in our favour” — but never with a full noun phrase.
• εναντίον την κυβέρνηση -> εναντίον της κυβέρνησης — likewise εναντίον; the accusative version is ενάντια στην κυβέρνηση.
• εναντίον εμένα -> εναντίον μου — a pronoun after these prepositions is the weak genitive clitic, not a strong form.
• υπέρ εμάς -> υπέρ μας — same rule in the plural.
• κατά της συνάντησης meaning “during the meeting” -> κατά τη συνάντηση — genitive κατά means “against”; “during” needs the accusative.
• περί το θέμα meaning “about the matter” -> περί του θέματος — accusative περί means “roughly, around”.
• άνευ προϋποθέσεις -> άνευ προϋποθέσεων — the plural noun needs the genitive plural.
• μετά χαρά -> μετά χαράς — a frozen genitive; never re-cast it as an accusative.
• μεταξύ μου και του Νίκου -> μεταξύ μας (or ανάμεσα σε μένα και στον Νίκο) — μεταξύ happily joins two nouns (μεταξύ Ελλάδας και Ιταλίας), but it cannot join a clitic to a noun.
• κατόπιν αιτήματος σας -> κατόπιν αιτήματός σας — a word stressed on the third-from-last syllable adds a second accent before a clitic.

Tips

• Use the substitution test before you write one: if λόγω can be swapped for εξαιτίας, άνευ for χωρίς, προ for πριν από, and the sentence still says the same thing, you have the right preposition — and if the plain twin sounds better in context, use the twin.
• Fix the case with the clitic test. Say the phrase with a pronoun: εναντίον μου proves the genitive, ενάντια σε μένα proves the accusative. If neither sounds right, the preposition is probably not the one you want.
• For κατά and περί, decide the meaning first, then pick the case: “against / about” pulls the genitive, “during, according to / roughly, around” pulls the accusative.
• Keep the register consistent inside the sentence. Άνευ σοβαρού λόγου is fine in a report; άνευ παρέας in a text message to a friend is a joke. Bare άνευ, with nothing after it, is the one exception — it has genuinely slipped into casual speech: Θέλεις την πίτσα σου με ελιές ή άνευ;
• Πλην is the narrowest of the set. Its genitive is essentially fixed (πλην τούτου, πλην των άλλων, πλην ενός), and in the arithmetical sense “minus” it simply stands between two bare numerals: δέκα πλην τρία. For a free “except for”, εκτός από is the safe choice.
• Remember the spelling split of εκ / εξ: consonant follows εκ (εκ νέου, εκ μέρους), vowel follows εξ (εξ αρχής, εξ ολοκλήρου).
• Collect them through their verbs. Once you connect εις-, εκ-, συν-, περί-, υπέρ- with εισάγω, εξάγω, συνεργάζομαι, περιγράφω, υπερασπίζομαι, the prepositions stop feeling foreign and the vocabulary comes for free.
• In formal documents expect the learned genitive singular in -εως right after them (κατόπιν συνεννοήσεως, εξ αποστάσεως); recognise it, and use the plain -ης form when in doubt.