Greek has a second relative pronoun, and it is the mirror image of the first. Where που is one syllable that never changes and tells you nothing, ο οποίος is a full adjective-shaped word that changes eighteen ways and tells you everything: the gender and number of what it stands for, and the grammatical role it plays inside its own clause. It is built out of the definite article plus οποίος, and the article is not decoration — it is part of the word.
Two agreements pull on it at once, from opposite directions, and separating them is the whole skill. Gender and number come from the antecedent, outside the clause. Case comes from the role, inside the clause. Get that straight and the paradigm is mechanical.
The paradigm
| Masculine | Feminine | Neuter | |
|---|---|---|---|
| Nom. sg. | ο οποίος | η οποία | το οποίο |
| Gen. sg. | του οποίου | της οποίας | του οποίου |
| Acc. sg. | τον οποίο(ν) | την οποία | το οποίο |
| Nom. pl. | οι οποίοι | οι οποίες | τα οποία |
| Gen. pl. | των οποίων | των οποίων | των οποίων |
| Acc. pl. | τους οποίους | τις οποίες | τα οποία |
It declines exactly like an ordinary -ος / -α / -ο adjective, with the stress fixed on the -οι- throughout, and the genitive plural των οποίων is one form for all three genders. There is nothing irregular to memorise. What has to become automatic is the two-step: read the antecedent for gender and number, read the verb for case.
Ο υπουργός, ο οποίος βρίσκεται στις Βρυξέλλες, δεν σχολίασε τίποτα.
o ipurghós, o opíos vrískete stis Vrikséles, dhen scholíase típota
The minister, who is in Brussels, made no comment. (formal / journalistic)
Η πρόταση την οποία κατέθεσε η αντιπολίτευση απορρίφθηκε.
i prótasi tin opía katéthese i andipolítefsi aporífthike
The motion which the opposition tabled was rejected. (formal)
Τα μέτρα τα οποία ανακοινώθηκαν χθες ισχύουν από τον Σεπτέμβριο.
ta métra ta opía anakinóthikan chthes ischíun apó ton Septémvrio
The measures announced yesterday apply from September. (formal / journalistic)
The two agreements, worked through
Take a feminine singular antecedent, η δημοσιογράφος, and change nothing but the verb of the relative clause. The gender and number stay put; the case moves.
| Role in the clause | Form | Phrase |
|---|---|---|
| subject | nominative | η δημοσιογράφος η οποία έγραψε το άρθρο |
| direct object | accusative | η δημοσιογράφος την οποία κάλεσαν |
| possessor | genitive | η δημοσιογράφος της οποίας το άρθρο… |
| after a preposition | accusative | η δημοσιογράφος στην οποία μίλησε |
Ο φοιτητής τον οποίο συνάντησα στη βιβλιοθήκη μου έδωσε τις σημειώσεις του.
o fititís ton opío sinándisa sti vivliothíki mu édhose tis simiósis tu
The student I ran into in the library gave me his notes. (formal)
Οι κάτοικοι, οι οποίοι διαμαρτύρονται εδώ και μήνες, ζητούν συνάντηση με τον δήμαρχο.
i kátiki, i opíi dhiamartíronde edhó ke mínes, zitún sinándisi me ton dhímarcho
The residents, who have been protesting for months, are asking for a meeting with the mayor. (journalistic)
The last row of the table is where ο οποίος does work που simply cannot do on its own, because a preposition cannot govern που. That whole territory — με τον οποίο, στην οποία, για τους οποίους — has its own page: relatives after prepositions. Here it is enough to note that the case after a preposition is the accusative, exactly as it is for any noun.
The genitive: how Greek says "whose"
English whose is a single invariable word, and this is where English speakers make their most consistent mistake with ο οποίος. The Greek genitive agrees with the possessor — the thing the antecedent is — in gender and number. A feminine possessor takes της οποίας, a masculine or neuter one του οποίου, a plural one των οποίων, and none of that has anything to do with the possessed noun that follows.
Η εταιρεία της οποίας ο διευθυντής παραιτήθηκε βρίσκεται υπό έρευνα.
i etería tis opías o dhiefthindís paretíthike vrískete ipó érevna
The company whose director resigned is under investigation. (formal)
Ο συγγραφέας του οποίου το πρώτο βιβλίο έγινε ταινία ζει στην Κρήτη.
o singraféas tu opíu to próto vivlío éyine tenía zi stin Kríti
The writer whose first book was made into a film lives in Crete. (formal)
Πρόκειται για ένα φαινόμενο οι αιτίες του οποίου παραμένουν άγνωστες.
prókite ya éna fenómeno i etíes tu opíu paraménun ághnostes
This is a phenomenon whose causes remain unknown. (academic)
Look at the word order in those three. The first two put the genitive in front of the possessed phrase — της οποίας ο διευθυντής — which is the opposite of an ordinary Greek possessive (ο διευθυντής της εταιρείας, possessor second). The third puts it after: οι αιτίες του οποίου. Both orders are correct and both are common in careful prose; the fronted one is a little tighter and is what you will meet most often in journalism. What you cannot do is separate the article from οποίου, or leave the genitive out and hope the possession is inferred.
Where it actually lives
ο οποίος is not a "more correct" relative. It is a register-marked one, and its natural habitats are narrow and identifiable:
- Journalism — where sentences carry a lot of named entities and the reader must not lose track of which one the clause is about.
- Academic and technical prose — where the antecedent is often several words back behind a chain of modifiers.
- Law and official documents — where ambiguity has consequences and where the form also carries the institutional tone the genre expects.
- Careful speech in exactly the same situations: a lecture, a courtroom, a formal apology.
Το νομοσχέδιο, το οποίο ψηφίστηκε με μεγάλη πλειοψηφία, τίθεται σε ισχύ τον Ιανουάριο.
to nomoschédhio, to opío psifístike me megháli pliopsifía, títhete se ischí ton Ianuário
The bill, which passed with a large majority, comes into force in January. (legal / journalistic)
Τα δικαιολογητικά, τα οποία αναφέρονται παρακάτω, κατατίθενται εις διπλούν.
ta dhikeoloyitiká, ta opía anaféronde parakáto, katatíthende is dhiplún
The supporting documents listed below are to be submitted in duplicate. (legal / official)
That second sentence shows the form in its most institutional setting, alongside the frozen archaism εις διπλούν. It also shows a habit of official Greek worth recognising: the relative clause pointing forward, to a list that has not appeared yet. More of that register's furniture is on formal connectors.
What ο οποίος cannot do
The form is heavier than που but it is not more powerful, and there are jobs it simply cannot take. It needs a noun phrase as its antecedent, so it cannot attach to a time or place expression the way που can: τώρα που ήρθες, εκεί που δουλεύω, τη φορά που τον είδα have no ο οποίος version at all. It also has no business in a complement clause — Χαίρομαι που ήρθες uses a completely different που, and swapping in a relative pronoun produces nonsense. When the two forms genuinely compete and how to choose is the subject of που vs ο οποίος.
Common Mistakes
1. Taking the case from the antecedent instead of from the role. The commonest structural error, and it is invisible to an English speaker because English marks none of this.
❌ Η επιτροπή κάλεσε τη γυναίκα την οποία υπέβαλε την καταγγελία.
Incorrect — she is the subject of υπέβαλε inside the clause, so the relative is nominative: η οποία υπέβαλε.
✅ Η επιτροπή κάλεσε τη γυναίκα η οποία υπέβαλε την καταγγελία.
i epitropí kálese ti yinéka i opía ipévale tin katangelía
The committee summoned the woman who had filed the complaint.
2. Agreeing with the meaning instead of the grammatical gender. Τα παιδιά are people, so English reaches for a person-shaped word; Greek reaches for the neuter, because the noun is neuter.
❌ Τα παιδιά, οι οποίοι έλειπαν, θα δώσουν εξετάσεις τον Σεπτέμβριο.
Incorrect — παιδιά is neuter plural, so the relative is τα οποία, whatever the sex of the children.
✅ Τα παιδιά, τα οποία έλειπαν λόγω γρίπης, θα δώσουν εξετάσεις τον Σεπτέμβριο.
ta pedhiá, ta opía élipan lógho ghrípis, tha dhósun eksetásis ton Septémvrio
The children, who were absent with flu, will sit the exams in September.
3. Treating "whose" as invariable. English gives you one word for every possessor; Greek makes you choose a gender and a number.
❌ Η ομάδα του οποίου ο προπονητής αποχώρησε έχασε και το επόμενο ματς.
Incorrect — the possessor ομάδα is feminine singular, so the genitive is της οποίας.
✅ Η ομάδα της οποίας ο προπονητής αποχώρησε έχασε και το επόμενο ματς.
i omádha tis opías o proponitís apochórise échase ke to epómeno mats
The team whose coach walked out lost the next match as well.
4. Confusing ο οποίος with όποιος. One letter of spacing apart, and completely different jobs: ο οποίος needs an antecedent, όποιος ("whoever") has its own built in.
❌ Ο οποίος θέλει να έρθει, ας δηλώσει συμμετοχή μέχρι την Παρασκευή.
Incorrect — with no antecedent you need the free relative όποιος: Όποιος θέλει να έρθει.
✅ Όποιος θέλει να έρθει, ας δηλώσει συμμετοχή μέχρι την Παρασκευή.
ópios théli na érthi, as dhilósi simetochí méchri tin Paraskeví
Anyone who wants to come should register by Friday.
5. Dropping the article. οποίος on its own is not a word of modern Greek; the article is part of the pronoun and goes everywhere with it.
❌ Ο πελάτης, οποίος διαμαρτυρήθηκε γραπτώς, πήρε τα λεφτά του πίσω.
Incorrect — the definite article is obligatory: ο οποίος, τον οποίο, της οποίας.
✅ Ο πελάτης, ο οποίος διαμαρτυρήθηκε γραπτώς, πήρε τα λεφτά του πίσω.
o pelátis, o opíos dhiamartiríthike ghraptós, píre ta leftá tu píso
The customer, who complained in writing, got his money back.
Key Takeaways
- ο οποίος / η οποία / το οποίο declines like an ordinary -ος / -α / -ο adjective, with the stress fixed on -οι- and one genitive plural, των οποίων, for all genders.
- Gender and number come from the antecedent; case comes from the role inside the relative clause. These are two independent decisions and must be made separately.
- The definite article is part of the pronoun — never ×οποίος on its own.
- The genitive translates English whose and agrees with the possessor: της οποίας ο διευθυντής, του οποίου το βιβλίο, των οποίων οι αιτίες. Both orders (genitive before or after the possessed phrase) are correct.
- Its register is journalism, academic prose, law and official documents, plus careful speech in those same settings — not "better Greek".
- It needs a noun-phrase antecedent: there is no ο οποίος version of τώρα που, εκεί που or the complementiser που.
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Start learning Greek →Related Topics
- 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.
- 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.
- που vs ο οποίοςB2 — Both are correct Greek and the axis between them is register plus explicitness, not right and wrong: που is light, invariable and covers nine sentences out of ten; ο οποίος marks gender, number and case, which buys you clarity in writing and costs you naturalness in speech. A context-by-context table, the two places where the choice disappears, how ο οποίος fixes an ambiguous attachment, and why piling on ο οποίος in conversation backfires.