In short

Greek word order is free, but it is not random. Because case endings mark who does what, position is left free to mark something else: what the sentence is about (the topic) and what is newsworthy in it (the focus). An object topic moved to the front is obligatorily picked up again by a weak pronoun inside the clause (Τον Γιάννη τον είδα χθες); a contrastively fronted focus is never doubled (ΤΟΝ ΓΙΑΝΝΗ είδα, όχι τη Μαρία). Everything else may float, except the preverbal cluster δεν θα / να μην / ας μην - genitive clitic - accusative clitic - verb, which is welded shut.

The rule

Case marks function, position marks information. The three sentences below all say that Yannis saw Maria, because ο Γιάννης is nominative and τη Μαρία accusative in every one of them:

• Ο Γιάννης είδε τη Μαρία. — neutral SVO; you are telling me what Yannis did.
• Είδε τη Μαρία ο Γιάννης. — VOS; the whole event is new, the subject arrives last as the informative part.
• Τη Μαρία την είδε ο Γιάννης. — the object is the topic (“as for Maria…”), so it is fronted and resumed by την.

An English speaker’s instinct is to read the first noun as the subject. Greek gives you no such licence: read the article and the ending, not the slot.

Topic (θέμα): front it and double it. A referent that is already known, or that you are switching the conversation to, goes to the left edge of the clause. When that referent is an object, the clause must still contain its weak pronoun, agreeing in gender, number and case. This is κλιτικός αναδιπλασιασμός, clitic doubling:

• Τον Γιάννη τον είδα χθες. (accusative object, doubled by τον)
• Της Μαρίας της το έδωσα. (indirect object in the genitive, doubled by της; το is the direct-object clitic)
• Το ψωμί το αγόρασα, το γάλα το ξέχασα.

Leave the clitic out and the sentence does not become “slightly less good” — it changes meaning, and is read as focus.

Focus (εστίαση): front it and leave it bare. A constituent that corrects, contrasts or answers a question is fronted with no doubling, and in speech carries the main pitch accent:

• Τον Γιάννη είδα, όχι τη Μαρία. — “It was Yannis I saw.”
• Αύριο φεύγουμε, όχι σήμερα.
• — Ποιον περιμένεις; — Τον διευθυντή περιμένω.

So the presence or absence of one small word is the whole difference: Τον Γιάννη τον είδα = topic (“as for Yannis, I saw him”); Τον Γιάννη είδα = focus (“Yannis is who I saw”).

Right dislocation (δεξιά μετατόπιση). The same doubling works backwards. Start with the clitic, then add the full phrase as an afterthought at the end, usually to clarify or to soften:

• Τον είδα χθες, τον Γιάννη.
• Της το έστειλα ήδη, της Μαρίας.

Presentational order: verb first. A brand-new, indefinite participant is not announced in subject position. Greek presents it after the verb: Ήρθε ένας άντρας και σε ζήτησε. Ένας άντρας ήρθε is not ungrammatical, but it presupposes that we already had a particular man in mind.

The preverbal cluster is rigid. All the freedom above stops at the verb. With a finite verb, weak pronouns stand before it, in a fixed chain that admits nothing between its links:

δεν → θα → genitive clitic → accusative clitic → verb να / ας → μην → genitive clitic → accusative clitic → verb μην → genitive clitic → accusative clitic → verb

Watch where the negation sits: δεν comes before θα, but μην comes after να and ας, never the other way round. Δεν θα σου το πω. Να μου το δώσεις. Να μην μου το πεις. Ας τους τα στείλουμε. Μην μας το ξαναπείς. Adverbs, subjects and everything else must stand outside the chain: Δεν θα σου το πω αύριο (not inside it). Only the imperative and the gerund put the pronouns after the verb: Δώσε μού το. Βλέποντάς τον, χαμογέλασα.

Strong object pronouns are doubled. A stressed object pronoun (εμένα, εσένα, αυτόν) does not stand alone: Εμένα μου το είπε. Εσένα σε περιμένουν. The exception is the focus rule above: a strong pronoun that is itself the contrast stays bare (ΕΜΕΝΑ ρώτησαν, όχι εσένα).

Forms & patterns

Case, not position, identifies the participants. Note the stress shift in the genitive plural.

The weak (αδύνατοι) pronouns that do the doubling:

The preverbal cluster, slot by slot:

The cluster keeps its shape through all six persons:

The same proposition, four packagings:

Examples

Common mistakes

• Τον Γιάννη είδα χθες (meaning “as for Yannis, I saw him”) -> Τον Γιάννη τον είδα χθες — a fronted topic must be resumed by a clitic; without it the hearer reads contrast (“Yannis is the one I saw”).
• Τον Γιάννη τον είδα, όχι τη Μαρία -> Τον Γιάννη είδα, όχι τη Μαρία — contrastive focus is never doubled; the clitic cancels the contrast.
• Της Μαρίας έδωσα το κλειδί (as a topic) -> Της Μαρίας της έδωσα το κλειδί — a fronted genitive object needs its genitive clitic just as an accusative one does.
• Ο Γιάννης είδε η Μαρία -> Ο Γιάννης είδε τη Μαρία — function comes from the case, not the slot; a second nominative is read as a second subject, not as an object.
• Είδα τον στην αγορά -> Τον είδα στην αγορά — with an indicative verb the weak pronoun stands before it; postverbal pronouns belong only to the imperative and the gerund.
• Δεν σου θα το πω -> Δεν θα σου το πω — the slots are ordered άρνηση/μόριο, θα ή μην, γενική, αιτιατική, ρήμα, and never swap.
• Θα δεν σου το πω -> Δεν θα σου το πω — δεν stands outside θα, at the very front of the cluster. With να and ας it is the other way round: μην να μου το πεις -> να μην μου το πεις.
• Δεν θα σου το αύριο πω -> Δεν θα σου το πω αύριο — nothing may be inserted inside the cluster, not even a one-word adverb.
• Δεν θα το σου πω -> Δεν θα σου το πω — the genitive (indirect) clitic precedes the accusative (direct) one.
• Ένας άντρας ήρθε και σε ζήτησε (introducing a stranger) -> Ήρθε ένας άντρας και σε ζήτησε — brand-new indefinite participants are presented after the verb.
• Εμένα το είπαν πρώτα -> Εμένα μου το είπαν πρώτα — a strong object pronoun needs its weak twin in the clause, unless it is itself the contrastive focus.

Tips

• Ask yourself one question before you front anything: old or new? Old and already in play = topic, so front it and double it. New, corrective or the answer to a question word = focus, so front it and leave it bare.
• The doubling clitic agrees with the fronted phrase in gender, number and case: τον Γιάννη → τον, τη Μαρία → την, τα παιδιά → τα, της Μαρίας → της.
• Doubling likes definite, specific objects (τον καφέ, το γράμμα σου, τον διευθυντή). Bare indefinites are not doubled: you say Αγόρασα ένα βιβλίο, not a doubled version of it.
• Learn the cluster as a single phonological word: δεν-θα-σου-το-πω. If you can hear it as one chunk, you will never drop an adverb into the middle of it.
• The verb-first order is the normal narrative and news-headline order (Έφτασε η άνοιξη, Ξεκίνησαν οι εργασίες), so do not read it as poetic inversion.
• Since the subject is usually dropped when it is the topic, most real sentences fill only the object and adverb slots — see pro-drop.
• In writing, focus is often marked with capitals or italics; a word in ALL CAPITALS drops its accent (ΤΟΝ ΓΙΑΝΝΗ) by normal Greek convention. Where the pronouns follow the verb, the extra accent obeys the three-syllable law, not their number: read verb and clitics as one word, and if its stress then falls outside the last three syllables, a second accent is added — on the verb’s own final syllable (Βλέποντάς τον), or on the first clitic when two of them follow an imperative (Δώσε μού το). While the stress stays inside the last three syllables nothing is added: Πάρε το, Μιλώντας του.