If you want an easy win in Greek noun declension, start here. Neuter nouns ending in -ο — το βιβλίο (the book), το νερό (the water), το αυτοκίνητο (the car) — are among the first nouns you meet, and they behave with unusual generosity: three of the four cases look exactly the same. This page shows you the full paradigm, the one form you actually have to learn (the genitive), and the single accent trap that catches learners.
The one thing that makes neuters easy: nom = acc = voc
In Greek, every noun has four cases — nominative (the subject), accusative (the direct object), genitive (possession, "of"), and vocative (calling out to someone). For masculine and feminine nouns those cases often differ, so you have to track which form goes where. Neuters throw that worry out: the nominative, accusative and vocative are always identical, in both the singular and the plural. That's true of every neuter class in the language, not just the -ο one.
The practical upshot: in the singular, only the genitive has its own shape. Learn the nominative, and you already know the accusative and the vocative for free.
Το βιβλίο που μου δάνεισες ήταν καταπληκτικό.
to vivlío pu mu dhánises ítan katapliktikó
The book you lent me was fantastic. (nominative — subject)
Διαβάζω το βιβλίο στο τρένο.
dhiavázo to vivlío sto tréno
I read the book on the train. (accusative — object, same form)
Notice that English does the same thing with word order — "the book" looks identical whether it's the subject or the object. A Greek masculine noun would change (ο φίλος → τον φίλο), but the neuter το βιβλίο stays put. So the neuter is, if anything, closer to how English behaves than the other genders are.
The singular paradigm
The endings are: -ο for nominative / accusative / vocative, and -ου for the genitive. Here is το βιβλίο in full:
| Case | Singular | Plural |
|---|---|---|
| Nominative | το βιβλίο | τα βιβλία |
| Genitive | του βιβλίου | των βιβλίων |
| Accusative | το βιβλίο | τα βιβλία |
| Vocative | βιβλίο | βιβλία |
The article changes with the case just as much as the noun does — το (nom/acc), του (gen sing), τα (nom/acc plural), των (gen plural). Always store a neuter noun with its το, because the article is what tells you the gender.
Η τιμή του βιβλίου είναι δέκα ευρώ.
i timí tu vivlíu íne dhéka evró
The price of the book is ten euros. (genitive singular)
Το νερό της βρύσης εδώ πίνεται μια χαρά.
to neró tis vrísis edhó pínete mia chará
The tap water here is perfectly fine to drink.
Το αυτοκίνητό μου δεν παίρνει μπροστά.
to aftokínitó mu dhen pérni brostá
My car won't start.
(That το αυτοκίνητό carries a second accent because the little word μου leans onto it — a separate topic, but don't let the double accent confuse you; the noun is still just αυτοκίνητο.)
The plural: nom/acc -α, genitive -ων
In the plural, neuters in -ο take -α for nominative / accusative / vocative and -ων for the genitive. So το βιβλίο → τα βιβλία, and "of the books" is των βιβλίων.
Έβαλα όλα τα βιβλία μέσα στην τσάντα.
évala óla ta vivlía mésa stin tsánda
I put all the books inside the bag.
Η τιμή των βιβλίων ανέβηκε φέτος.
i timí ton vivlíon anévike fétos
The price of the books went up this year. (genitive plural)
Τα δέντρα στην αυλή έχασαν τα φύλλα τους.
ta dhéndra stin avlí échasan ta fíla tus
The trees in the yard lost their leaves.
Τα νερά της λίμνης είναι κρύα ακόμα και το καλοκαίρι.
ta nerá tis límnis íne kría akóma ke to kalokéri
The lake's waters are cold even in summer.
A tip for English speakers: don't reach for an -s. Greek marks plurality by changing the ending, not by adding a suffix on top — βιβλίο → βιβλία, δέντρο → δέντρα. The -α ending on a neuter noun is a plural, even though the very similar-looking -α on a feminine noun (η ώρα) is a singular. Context and the article (τα vs η) keep them apart.
The accent trap: proparoxytone genitives shift
Here is the one wrinkle. Most -ο nouns keep their accent in the same place throughout the paradigm — βιβλίο → βιβλίου → βιβλία → βιβλίων never moves off the ί. But when a word is stressed on the third-from-last syllable (a proparoxytone, like αυτοκίνητο), the genitive pulls the accent one step toward the ending:
| Case | Singular | Plural |
|---|---|---|
| Nominative | το αυτοκίνητο | τα αυτοκίνητα |
| Genitive | του αυτοκινήτου | των αυτοκινήτων |
| Accusative | το αυτοκίνητο | τα αυτοκίνητα |
| Vocative | αυτοκίνητο | αυτοκίνητα |
Watch the stressed syllable move: αυτοκίνητο (on -κί-) → αυτοκινήτου / αυτοκινήτων (on -νή-). The nominative and accusative plural (τα αυτοκίνητα) keep the original accent; only the two genitives shift. The same happens with το πρόσωπο → του προσώπου (face/person) and το άτομο → του ατόμου (individual).
Why only the genitives? Not because the word ran out of room — count the syllables and you will see that αυ-το-κί-νη-το and αυ-το-κι-νή-του have exactly the same number, and third-from-last stress would have been perfectly legal in ×αυτοκίνητου. The real reason is the weight of the ending: the genitive -ου and -ων are historically long, and Greek forbids a third-from-last accent in front of a long final syllable. The plural -α is light, which is precisely why τα αυτοκίνητα leaves the accent alone. This is the same law that gives ο άνθρωπος → του ανθρώπου in the masculine, and it is set out in full on accent shift in declension.
Τα φώτα του αυτοκινήτου έμειναν αναμμένα όλη νύχτα.
ta fóta tu aftokinítu éminan anaména óli níchta
The car's lights were left on all night. (accent shifted to -νή-)
But everyday words refuse to shift
Now the part most textbooks leave out, and the reason learners get corrected by real Greeks. In the modern language this shift survives as a property of the register a word belongs to, not as a rule speakers still apply across the board. Words that came down the learned, written channel take it without complaint (formal / learned): του προσώπου, του θεάτρου, του αυτοκινήτου, του επιπέδου. But homely, thoroughly demotic neuters simply refuse to move, and the unshifted form is the standard one (informal, and normal in writing too): του σύννεφου (cloud), του πρόβατου (sheep), του σίδερου (iron). ×Του συννέφου is not something a Greek speaker says; it reads as stiff, katharévousa-flavoured writing.
Το σχήμα του σύννεφου έμοιαζε με καράβι.
to schíma tu sínefu émiaze me karávi
The shape of the cloud looked like a ship.
Η έκφραση του προσώπου της τα έλεγε όλα.
i ékfrasi tu prosópu tis ta éleye óla
The expression on her face said it all. (learned word — shift applies)
A quick contrast with the other neuter classes
Neuter -ο is only one of several neuter families. Its close cousins are the -ι nouns (το παιδί, το σπίτι) and the -μα nouns (το πρόβλημα, το όνομα). All three share the golden rule — nom = acc = voc — but they differ in their genitive and plural endings. The -ο class is the plainest of the three, which is exactly why it's the place to start.
Common Mistakes
❌ Ο βιβλίο είναι καινούριος.
Incorrect — wrong article and adjective agreement; βιβλίο is neuter, not masculine.
✅ Το βιβλίο είναι καινούριο.
to vivlío íne kenúrio
The book is new.
Because the ending -ο can look like a masculine ending to a beginner, learners reach for ο and make the adjective agree as masculine. It's neuter: το βιβλίο, καινούριο.
❌ Διαβάζω το βιβλίου κάθε βράδυ.
Incorrect — the object needs the plain -ο form, not the genitive -ου.
✅ Διαβάζω το βιβλίο κάθε βράδυ.
dhiavázo to vivlío káthe vrádhi
I read the book every evening.
The direct object is the accusative, which for a neuter is identical to the nominative (-ο). Don't swap in the genitive -ου just because the noun isn't the subject.
❌ Μου αρέσει πολύ το χρώμα του αυτοκίνητου σου.
Incorrect — αυτοκίνητο is a learned proparoxytone, so the genitive shifts: αυτοκινήτου.
✅ Μου αρέσει πολύ το χρώμα του αυτοκινήτου σου.
mu arési polí to chróma tu aftokinítu su
I really like the colour of your car.
❌ Αγόρασα καινούρια βιβλίες.
Incorrect — the neuter plural is -α, not -ες.
✅ Αγόρασα καινούρια βιβλία.
aghórasa kenúria vivlía
I bought new books.
The -ες plural belongs to feminine and masculine nouns. Neuters in -ο pluralise with -α: βιβλίο → βιβλία, δέντρο → δέντρα, αυτοκίνητο → αυτοκίνητα.
Key Takeaways
- Nom = acc = voc, always. In the singular, only the genitive (-ου) is a separate form.
- Plural: -α for nom/acc/voc, -ων for the genitive.
- Store every neuter noun with το, because the ending -ο alone won't always tell you the gender.
- Learned proparoxytones (αυτοκίνητο, πρόσωπο, θέατρο) shift the accent in the genitive: του αυτοκινήτου, των αυτοκινήτων — because -ου / -ων are historically long, not because a syllable was added.
- Everyday demotic proparoxytones resist the shift: του σύννεφου, του πρόβατου, του σίδερου — not ×του συννέφου.
- Mark the object with the plain -ο form, not -ου — the accusative equals the nominative.
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Start learning Greek →Related Topics
- Neuter Nouns in -ιA1 — Neuter nouns like το παιδί and το σπίτι, whose genitive -ιού and plural -ια are pronounced as a single glide (παιδιά = 'pedhyá'). Home of the everyday diminutive -άκι.
- Accusative: The Direct ObjectA1 — The accusative is the case of the thing the verb acts on — Βλέπω τον Γιάννη, Τρώω το μήλο — marked by the article (ο→τον, η→την, οι→τους/τις) rather than by position, which is exactly why Greek word order can move around so freely.
- Neuter Nouns in -μαA2 — The productive -μα class (το πρόβλημα, το όνομα, το γράμμα) whose real stem is the hidden -ματ- that surfaces in every case except the nominative: το όνομα → του ονόματος. Miss the -ματ- and you say *του ονόμα.
- The Three GendersA1 — Every Greek noun is masculine, feminine, or neuter — and that gender, shown by its article ο / η / το, controls the adjectives and pronouns around it, so you learn each noun together with its article, not on its own.
- Forming the PluralB1 — One reference for every plural ending in Greek — masculine -οι / -ες / -άδες / -ηδες, feminine -ες / -άδες / -ούδες / -εις / -οι, neuter -α / -ια / -ματα / -η — with the two rules that decide which -ας and which -ης noun goes where, plus the classic trap where a neuter plural in -α (τα παιδιά, 'the children') is mistaken for a feminine singular.
- Accent Shift in DeclensionB1 — Why the stress jumps forward when you decline a noun — άνθρωπος but του ανθρώπου, αυτοκίνητο but του αυτοκινήτου, κυβέρνηση but των κυβερνήσεων. The three-syllable law applied systematically, gender by gender, with tables showing exactly which cells move.