In short

English juggles who, whom, whose, which, that and where. Everyday Greek uses one word for all of them: που, unaccented and unchanging. It never agrees with anything and it never declines, whatever the gender, number or case of the noun it hangs on, and whatever job that noun does inside the clause.

The price of that simplicity is small and mechanical: when the noun would have needed a case που cannot show — an indirect object, a possessor, an object of a preposition — Greek puts an ordinary weak pronoun inside the clause to carry it: ο φίλος που του έδωσα τα κλειδιά.

And keep it apart from its two lookalikes. The relative που wears no accent. The question word πού “where?” (lesson 12) always does. The conjunction που “that” after verbs of emotion (lesson 36) is a third word again — unaccented like the relative, but introducing a complement, not describing a noun.

The rule

A relative clause modifies a noun that has already been said (the antecedent), and in Greek it follows that noun immediately:

ο άντρας που ήρθε — the man who came

The linker is που in all of these situations:

• Subject of the clause: ο άντρας που ήρθε, τα παιδιά που παίζουν.
• Direct object of the clause: το βιβλίο που διάβασα, οι φίλοι που κάλεσα.
• Time or place adjunct: τη μέρα που γνωριστήκαμε, το χωριό που μεγάλωσα.

In those three cases nothing else is needed — the clause is complete as it stands.

The resumptive pronoun. Because που has no case of its own, some roles cannot be expressed by που alone. Greek then leaves που as a plain link and marks the role with a weak pronoun inside the clause, exactly where that pronoun would stand in an ordinary sentence:

• indirect object → weak genitive: η γυναίκα που της μιλούσες
• possessor (“whose”) → weak genitive on the possessed noun: ο κύριος που ξέχασα το όνομά του
• object of a preposition → preposition + strong pronoun: το σπίτι που μένω σ’ αυτό

With a place or time antecedent the bare το σπίτι που μένω is in fact the ordinary form — που on its own already does the work of preposition + relative — and the added σ’ αυτό is colloquial reinforcement. With other prepositions (ο άνθρωπος που σου μίλησα γι’ αυτόν) the fuller version is what keeps the sentence clear.

Restrictive and non-restrictive. Without commas, the clause narrows down the antecedent — it says which ones you mean. Set off by commas, it merely adds information about an antecedent that is already identified. Compare:

• Οι μαθητές που διάβασαν πέρασαν. — only the ones who studied passed.
• Οι μαθητές, που διάβασαν, πέρασαν. — all of them passed; and, by the way, they had studied.

Proper names and other uniquely identified antecedents therefore take commas: ο Γιώργος, που μένει στη Θεσσαλονίκη, …

Three homographs, one spelling to watch. που (relative), πού (interrogative “where?”), and που (the conjunction “that”). Only the question word takes the accent — see the table below.

Forms & patterns

που is one form, for every antecedent. Nothing changes on the left-hand side of the clause:

The antecedent declines; που does not. The noun in front takes whatever case its own sentence demands — including the stress shift of proparoxytone masculines — while που sits unchanged behind it:

When is a resumptive pronoun needed?

The weak pronouns you will need inside the clause (full set, from lesson 10):

Three words that look alike:

Examples

Common mistakes

• Ο άντρας ποιος ήρθε -> Ο άντρας που ήρθε — ποιος is only a question word (“who?”, “which?”); English who does double duty, Greek ποιος does not.
• Η γυναίκα πού μιλάει -> Η γυναίκα που μιλάει — the accent is what makes πού a question; the relative is bare που.
• Ο φίλος που έδωσα τα κλειδιά -> Ο φίλος που του έδωσα τα κλειδιά — που cannot carry the genitive, so the weak pronoun του has to fill the indirect-object slot.
• Το κορίτσι που τη μιλούσες -> Το κορίτσι που της μιλούσες — μιλάω takes the weak genitive, not the accusative (lesson 34).
• Το βιβλίο που το διάβασα ήταν ωραίο -> Το βιβλίο που διάβασα ήταν ωραίο — a direct object needs no resumptive; the extra το duplicates the antecedent.
• Χαίρομαι πού ήρθες -> Χαίρομαι που ήρθες — after a verb of emotion this που means “that”; accented, it would say “where”.
• Ο Γιώργος που μένει στη Θεσσαλονίκη έρχεται αύριο -> Ο Γιώργος, που μένει στη Θεσσαλονίκη, έρχεται αύριο — without commas the clause claims to be picking one Γιώργος out of several.

Tips

• Remember που as “the relative with no hat”. If the word answers the question “where?”, it wears one: πού.
• To test for a resumptive, rebuild the clause as a stand-alone sentence with a normal pronoun. Έδωσα τα κλειδιά σε αυτόν → the pronoun is an indirect object, so it survives as του inside the relative clause. If what comes out is a plain direct object, drop it.
• Anything that would need to be declined sits on the noun in front of που, never on που itself — so build the main clause first, then attach the relative clause behind the noun.
• Commas carry the meaning that English gets from that versus which: no commas = narrowing down, commas = extra information.
• With a place or time antecedent the preposition and strong pronoun are normally left out altogether (το σπίτι που μένω) — που alone carries the prepositional sense. Both versions are correct; keep the full one when the clause is long or ambiguous, and with any other preposition.
• Keep που close to its noun. If a long phrase separates them, the sentence gets hard to parse and Greek prefers to restructure or switch to ο οποίος.
• ο οποίος (lesson 58) is the declined, formal alternative for writing; ό,τι, όποιος and όπου (lesson 46) are a different thing again — they carry their own antecedent inside them. Only όπου doubles as a headed relative after a noun of place (οι γειτονιές όπου έπαιζε).