In short

When a verb has both an indirect object (“to me”, “to her”) and a direct object (“it”, “them”), Greek can express both with weak pronouns at once. The two little words form a single block that behaves like one word: genitive first, accusative second — μου το έδωσε “he gave it to me”, της τα έστειλα “I sent them to her”.

That block never breaks apart and it has only two possible homes. Before the verb it sits inside a fixed frame: δεν / θα / να / ας / μη + genitive + accusative + verb (δεν θα σου το πω). After a positive imperative it hops behind the verb and takes an extra written accent (δώσε μού το). One extra habit of everyday speech: σου fuses with the following accusative — σου το becomes στο, which looks exactly like the preposition in στο σχολείο but has nothing to do with it.

The rule

1. Two slots, fixed order. The indirect object is a genitive clitic, the direct object an accusative clitic, and in front of the verb the genitive always comes first. English word order (“gave it to me”) is the opposite of Greek, so translating word by word produces the classic error *το μου έδωσε.

2. The accusative slot is third person. Combinations such as μου το, σου τα, της τον are free. But a cluster of genitive + με / σε is impossible: for “she introduced me to him” you keep the weak accusative and use a full prepositional phrase — Με σύστησε σε αυτόν, not *Του με σύστησε.

3. The preverbal block. In every ordinary clause the cluster leans forward onto the verb. The particles δεν, θα, να, ας and μη(ν) open the block and nothing may be inserted anywhere inside it:

δεν / θα / να / ας / μη(ν) · genitive · accusative · verb

So Δεν θα σου το πω, Θέλω να μου το δώσεις, Ας τους τα στείλουμε. Adverbs, subjects and objects go outside the block, never inside it: Μου το έδωσε χθες ο Νίκος.

4. After the positive imperative. A command with no negation puts the cluster behind the verb, normally still genitive first: Δώσε μού το. Πες μας την. When the imperative is stressed on its next-to-last syllable, verb plus two enclitics is stressed too far from the end, so the first clitic takes the second accent (δεύτερος τόνος): δώσε μού το, φέρε μάς τα. A one-syllable imperative needs no extra mark, because the stress still falls inside the last three syllables: πες μας την. Behind an imperative — and only there — the reverse order also exists, with the verb clipped and no second accent: δώσε μού το and δώσ’ το μου stand side by side, and likewise δείξε μάς το and δείξ’ το μας. Both are correct; the genitive-first order is the one to build on. One form also changes shape behind the verb: the feminine plural accusative is τις in front of the verb but τες after it (Ρώτησέ τες). The cluster follows a gerund in -οντας too, but there the extra accent lands on the verb itself, not on a clitic: Δίνοντάς μου το, έφυγε. As soon as the command turns negative it stops being an imperative (μη + subjunctive), so the cluster goes back in front: Μη μου το λες.

5. The σου fusion. In speech, and increasingly in informal writing, σου merges with the accusative that follows: σου το → στο, σου τη(ν) → στη(ν), σου τα → στα, σου τον → στον, σου τους → στους, σου τις → στις. Do not expect a dictionary to spell it for you: the reference dictionary records no written form of this fusion at all, writes the two words out in full (σου το, σου τα), and reserves the one-word στου, στο(ν), στη(ν), στις, στα for the preposition σε, which it says always drops its -ε before the τ- of the article and is written together with it as a single word. Στο είπα is “I told you so”, while Πάω στο σχολείο is σε + το, the preposition. Only the context tells them apart: a fused clitic sits next to a verb and has no noun after it. The unfused σου το είπα is always correct and is the safer choice in formal writing.

6. The disambiguating accent. Ο πατέρας μου το είπε means “my father said it” (μου is a possessive). Ο πατέρας μού το είπε means “the father told it to me”. When a genitive clitic could be misread as a possessive of the preceding noun, accent it — the rule you already met with «Ο πατέρας μού είπε…».

Forms & patterns

The weak pronoun, both cases, all persons

The whole cluster: genitive down the side, accusative across the top

One cluster through all six persons of the verb (αόριστος of δίνω, cluster της το)

Where the block goes

The imperative, positive against negative

Examples

Common mistakes

• το μου έδωσε -> μου το έδωσε — Greek is the mirror image of English here: in front of the verb, genitive first, accusative second, always.
• σε το έδωσα -> σου το έδωσα — the person who receives is genitive (σου), not accusative (σε).
• του με σύστησε -> με σύστησε σε αυτόν — μου/σου/του cannot be followed by the clitic με or σε; use the strong form with σε.
• μου χθες το έδωσε -> μου το έδωσε χθες — nothing may stand inside the cluster or between it and the verb.
• δεν σου θα το πω -> δεν θα σου το πω — δεν and θα open the block; the clitics come after both, right before the verb.
• μου το δώσε -> δώσε μού το — a positive imperative pushes the cluster behind the verb.
• δώσε μου το -> δώσε μού το — with two enclitics after the verb the first one must carry the second accent.
• μην πες μου το -> μη μου το πεις — a negated command is μη + subjunctive, so the clitics move back in front.
• Στο σχολείο είπα ότι… (meaning “I told you”) -> Στο είπα ότι… — the fused clitic στο is never followed by a noun; that would be the preposition.

Tips

• Learn the block as one rhythmic unit — μου-το, σου-τα, της-τον — and it will never come out in the wrong order.
• A quick check: if the English is “gave it to me”, the Greek reverses the two words. Say the Greek “to-me it” and you are right.
• The accusative half tells you the gender and number of the thing: το for a neuter (το βιβλίο), την for a feminine (την εφημερίδα), τα for neuter plurals (τα κλειδιά). Choose it from the noun you are replacing.
• Test the position with the negative: if you can put δεν in front, the cluster is preverbal. Only a bare positive command sends it to the back.
• Whenever an imperative stressed on its next-to-last syllable ends up with two clitics behind it, write the accent on the first one — δώσε μού το, δείξε τούς τα. Leaving it out is a spelling error, like any other missing accent.
• Read στο, στη, στα twice: noun after it means preposition (στο τραπέζι), verb around it means σου + article-like clitic (Στο έδωσα).
• In an essay or an email, prefer the unfused σου το, σου τα. Keep στο, στα for dialogue and speech.