The core distinction fits in one sentence: που is the default and ο οποίος is what you reach for when the sentence needs the case, the gender or the formality made visible. Neither is more correct than the other, and a learner who treats ο οποίος as the "proper" relative will write Greek that reads like a summons.
This page assumes you already know how each form is built — που and ο οποίος have their own pages, and none of that is repeated here. What follows is only the decision.
The trade-off, stated plainly
που is lighter and less explicit. One syllable, no agreement to compute, no article to attach. It tells the listener that a relative clause has started and nothing else. Everything else — which noun it refers to, what role it plays — has to be recovered from context or supplied by a pronoun inside the clause.
ο οποίος is heavier and more explicit. Two words, three genders, four cases. It names its antecedent by gender and number and announces its own role by case before the clause has even begun. That is real information, and in a long written sentence it is worth the weight.
Ο τύπος που μας πούλησε τα εισιτήρια είχε πει άλλη ώρα.
o típos pu mas púlise ta isitíria íche pi áli óra
The bloke who sold us the tickets had said a different time. (informal — spoken Greek would use nothing else here)
Ο υπάλληλος ο οποίος εξέδωσε τα εισιτήρια δεν είχε ενημερωθεί για την αλλαγή.
o ipálilos o opíos eksédhose ta isitíria dhen íche enimerothí ya tin alayí
The clerk who issued the tickets had not been informed of the change. (formal — a written complaint)
Same event, same grammatical structure, two registers. Nothing in the first sentence is sloppy and nothing in the second is pompous; they belong to different documents.
Context by context
| Context | Reach for |
|---|---|
| Conversation, messages, email to a friend | που, almost without exception |
| Subject or direct-object clause, any register | που — it needs no help here |
| Antecedent is a bare time or place adverb (τώρα, τότε, εκεί) | που — the only option |
| Journalism, academic prose, law, official letters | ο οποίος for at least the heavier clauses |
| Antecedent sits behind another noun and attachment is unclear | ο οποίος — the agreement disambiguates |
| Long non-restrictive clause in writing | ο οποίος, though που is also correct |
| After a preposition, in writing | ο οποίος: με τον οποίο, στην οποία |
| After a preposition, in speech | που plus a resumptive: που πήγα μαζί του |
| Translating English whose | either — see below |
| Two or three relative clauses in one sentence | alternate them, to keep the chain readable |
The "whose" decision
English whose is the one meaning where both Greek forms are in genuine everyday competition, because the light strategy is not a workaround here — it is what people say. που keeps its shape and drops a possessive clitic onto the possessed noun; ο οποίος goes into the genitive and agrees with the possessor.
Ο γείτονας που η κόρη του σπουδάζει στην Αγγλία πουλάει το σπίτι.
o yítonas pu i kóri tu spudházi stin Anglía pulái to spíti
The neighbour whose daughter is studying in England is selling the house. (informal — the everyday shape, and the one you should be able to produce first)
Ο ιδιοκτήτης του οποίου η κόρη σπουδάζει στο εξωτερικό πουλάει το ακίνητο.
o idhioktítis tu opíu i kóri spudházi sto eksoterikó pulái to akínito
The owner whose daughter is studying abroad is selling the property. (formal — an estate agent's listing or a legal notice)
The deciding factor is the same as everywhere else on this page, with one extra weight on the scale: the possessed noun phrase can get long, and once it does, a genitive announced up front (του οποίου η κόρη…) is easier to follow than a clitic the reader has to wait for. Short phrase, spoken register: που. Long phrase, written register: ο οποίος.
Where the choice disappears
Two rows of that table are not preferences at all.
Prepositions. που cannot be governed by a preposition, so με που, στο που, για που are impossible as relatives. Either the preposition attaches to ο οποίος, or the clause keeps που and puts the preposition inside it with a pronoun. Both strategies, paired sentence by sentence, are on relatives after prepositions — that is the page's whole job, and it is not repeated here.
Non-nominal antecedents. ο οποίος needs a noun phrase, so a bare time or place adverb — τώρα, τότε, εκεί — leaves only που. A time or place noun is a different matter: η πόλη στην οποία ζω and η μέρα κατά την οποία γεννήθηκε are ordinary formal Greek.
Την τελευταία φορά που μιλήσαμε, ήταν ακόμα στη Λάρισα.
tin teleftéa forá pu milísame, ítan akóma sti Lárisa
The last time we spoke, he was still in Larissa.
And a third case, which is not a choice because it is not a relative clause: the complementiser που after verbs of emotion (Χαίρομαι που…, Λυπάμαι που…, Θυμάμαι που…) is a conjunction that happens to be spelled the same way. No relative pronoun can stand there.
What ο οποίος buys you: attachment
Here is the one situation where the choice changes the meaning rather than the tone. When the antecedent is followed by a second noun — a genitive, a prepositional phrase — που can attach to either of them, and Greek gives the listener nothing to go on.
Μίλησα με τη γραμματέα του διευθυντή που μόλις γύρισε από άδεια.
mílisa me ti ghramatéa tu dhiefthindí pu mólis yírise apó ádhia
I spoke to the manager's secretary who has just got back from leave. (ambiguous in Greek exactly as in English — who was on leave?)
Μίλησα με τη γραμματέα του διευθυντή, η οποία μόλις γύρισε από άδεια.
mílisa me ti ghramatéa tu dhiefthindí, i opía mólis yírise apó ádhia
I spoke to the manager's secretary, who has just got back from leave. (η οποία is feminine — it can only be the secretary)
The second sentence is unambiguous because η οποία is feminine nominative singular and του διευθυντή is masculine genitive. The agreement does the pointing. This is why legal and academic Greek leans on the form so heavily: not for grandeur, but because a document that can be read two ways is a document that will be.
Why overusing ο οποίος backfires
Spoken Greek uses ο οποίος sparingly, and mostly for the two reasons above: a preposition, or a real risk of confusion. Deployed anywhere else in conversation it does not sound educated, it sounds like someone reading aloud from a form.
Θυμάσαι εκείνον τον φίλο μου που δούλευε στο λιμάνι;
thimáse ekínon ton fílo mu pu dhúleve sto limáni
Do you remember that friend of mine who used to work at the port? (informal — ο οποίος in this sentence would land like a court transcript)
In writing the calculation is different but the principle survives: variety, not maximum explicitness. A well-made Greek paragraph uses που for its simple clauses and saves ο οποίος for the clauses that earn it.
Ο δικηγόρος που ανέλαβε την υπόθεση ζήτησε τα έγγραφα στα οποία στηρίζεται η κατηγορία.
o dhikighóros pu anélave tin ipóthesi zítise ta éngrafa sta opía stirízete i katighoría
The lawyer who took on the case asked for the documents on which the charge rests. (both forms in one sentence: που for the plain subject clause, ο οποίος because a preposition is involved)
Common Mistakes
1. Reading the pair as right and wrong. This is the mistake that generates all the others. There is no correctness axis here — only a register axis.
Ο γιατρός που με χειρούργησε δουλεύει τώρα στην Πάτρα.
o yatrós pu me chirúryise dhulévi tóra stin Pátra
The doctor who operated on me works in Patras now. (informal — what you say to a friend)
Ο ιατρός ο οποίος διενήργησε την επέμβαση υπηρετεί πλέον στην Πάτρα.
o iatrós o opíos dhieníryise tin epémvasi ipiretí pléon stin Pátra
The physician who performed the procedure now serves in Patras. (formal — a medical record; the same facts, a different document)
2. Using ο οποίος with a time or place antecedent. The form requires a noun phrase, and τώρα, τότε, εκεί are not noun phrases.
❌ Τώρα ο οποίος τελείωσες, μπορούμε να φύγουμε.
Incorrect — ο οποίος has no antecedent to agree with here; only που can follow τώρα.
✅ Τώρα που τελείωσες, μπορούμε να φύγουμε επιτέλους.
tóra pu telíoses, borúme na fíghume epitélus
Now that you've finished, we can finally leave.
3. Swapping ο οποίος in for the complementiser που. Once you have learned that ο οποίος "is the formal που", it is tempting to upgrade every που in sight. The που after an emotion verb is a conjunction, not a relative.
❌ Λυπάμαι πολύ ο οποίος δεν μπόρεσα να έρθω στα γενέθλιά σου.
Incorrect — this που introduces a complement clause, not a relative clause; no relative pronoun is possible.
✅ Λυπάμαι πολύ που δεν μπόρεσα να έρθω στα γενέθλιά σου.
lipáme polí pu dhen bóresa na értho sta yenéthliá su
I'm really sorry I couldn't make it to your birthday.
4. Believing non-restrictive clauses require ο οποίος. They do not. Commas plus που is ordinary, natural Greek at every level of formality.
Ο θείος μου, που έχει το μαγαζί στη γωνία, μας κερνάει πάντα.
o thíos mu, pu échi to maghazí sti ghonía, mas kernái pánda
My uncle, who has the shop on the corner, always stands us a round. (neutral — the comma carries the non-restrictive reading on its own)
Ο θείος μου, ο οποίος διατηρεί κατάστημα στη γωνία, μας κερνάει πάντα.
o thíos mu, o opíos dhiatirí katástima sti ghonía, mas kernái pánda
My uncle, who keeps a shop on the corner, always stands us a round. (formal — and note that the vocabulary has to move up with the relative or the sentence sits badly)
5. Chaining three που-clauses. Grammatical, and hard to read. The fix is not to convert them all but to alternate.
Βρήκα το άρθρο που ανέφερες που μιλάει για τη μελέτη που βγήκε πέρσι.
vríka to árthro pu anéferes pu milái ya ti meléti pu vyíke pérsi
I found the article you mentioned that talks about the study that came out last year. (three που-clauses in a row — correct, but the reader loses the thread)
Βρήκα το άρθρο που ανέφερες· αναλύει τη μελέτη η οποία δημοσιεύτηκε πέρσι.
vríka to árthro pu anéferes· analíi ti meléti i opía dhimosiéftike pérsi
I found the article you mentioned; it analyses the study which was published last year. (one clause broken off, one relative of each kind — the chain is easy to follow)
Key Takeaways
- που is the default. Use it unless something in the sentence gives you a reason not to.
- The axis is register and explicitness, never correctness. A που sentence is not an informal version of a correct sentence; both forms are correct Greek.
- The choice disappears after a preposition (που cannot be governed by one) and disappears after a bare time or place adverb — τώρα, τότε, εκεί — which ο οποίος cannot attach to.
- ο οποίος earns its weight when it resolves an attachment ambiguity — its gender and number point at exactly one noun.
- In speech, ο οποίος outside its two justified contexts reads as reading aloud from a document, not as educated.
- Good written Greek alternates the two rather than maximising either.
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- The Relative πουA2 — One tiny word covers English who, whom, which and that, and it never changes shape: που is invariable for gender, number and case, so ο άντρας που ήρθε, η γυναίκα που ήρθε and τα παιδιά που ήρθαν all use the same form. Covers why που can never be dropped the way English drops 'that', the non-noun antecedents (τη μέρα που, τώρα που, εκεί που), restrictive against non-restrictive, and the person agreement in Εσύ που ξέρεις.
- The Relative ο οποίοςB2 — The declinable relative of written Greek: ο οποίος / η οποία / το οποίο takes its gender and number from the antecedent and its case from its own job inside the clause, so η εταιρεία της οποίας ο διευθυντής παραιτήθηκε is 'the company whose director resigned'. Full paradigm, the obligatory article, the genitive that translates English 'whose', and where the form actually lives — journalism, academic prose, law and official documents.
- Relatives After PrepositionsB2 — English offers 'the city in which I live' and 'the city I live in'; Greek offers η πόλη στην οποία ζω and η πόλη που ζω — and never the stranded preposition that sits at the end of the English one. The formal strategy (preposition + ο οποίος, including the genitive-governing λόγω / εξαιτίας / μέσω), the colloquial strategy (που plus a pronoun or adverb inside the clause), όπου for places, and paired versions of the same sentence in both.
- Resumptive Pronouns in που-ClausesC1 — Because που carries no case, a clitic inside the clause has to carry it instead: ο άνθρωπος που του μίλησα, η γυναίκα που της έδωσα το δώρο, ο συγγραφέας που διάβασα το βιβλίο του. The rule role by role — required for the genitive (indirect object and possessor) and for prepositional objects, absent for the subject and for a restrictive direct object, absent again for place and time — plus why this is not clitic doubling and where the clitic stands.