In short

Until 1976 Greece ran two written languages side by side: everyday δημοτική and the archaising καθαρεύουσα. Καθαρεύουσα lost, but it did not vanish - it left behind a few dozen frozen phrases that every speaker uses without thinking: εν τω μεταξύ, εντάξει, τοις εκατό, δόξα τω Θεώ, ούτως ή άλλως, εκ των προτέρων.

The single most important thing about them: they are vocabulary, not grammar. Several of them contain a dative - a case Modern Greek does not have. You memorise the whole string, spelling included, and you never take it apart to build a new one. There is no rule to generalise, only a list to recognise.

One learned pattern is still productive, though, and it is not the dative: the learned genitive (είναι της μόδας, είμαι της άποψης ότι, βιβλίο 300 σελίδων, του χρόνου). That part you can use creatively. Everything else on this page is a museum piece that happens to be in daily circulation.

The rule

1. Dative fossils are unanalysable. Modern Greek has four cases (ονομαστική, γενική, αιτιατική, κλητική). The dative died centuries ago. What survived is a closed set of adverbial phrases, mostly with εν, in which you can see ancient dative endings (-ω, -ει, -η, -οις) and the ancient dative article (τω, τη, τοις). They are inert: you cannot change the noun, add an adjective, or copy the pattern onto a new word. «Εν τω μεταξύ» is one word with spaces in it.

2. Adverbial fossils with εκ / εξ / ως, and frozen adverbs in -ως, behave the same way. εκ των προτέρων, εξ αρχής, ως εκ τούτου, ούτως ή άλλως. The case after εκ / εξ is a real genitive, so those look less alien - ως can take an accusative instead (ως επί το πλείστον), and an adverb pair like ούτως ή άλλως has no case at all - but all of them are still fixed strings, and the article inside them cannot be dropped or changed.

3. Register, not meaning, is what you choose. Most fossils have a plain demotic twin (διότι / γιατί, άνευ / χωρίς). The pair means the same thing; picking the learned member tells the listener something about the situation - a document, a news bulletin, a lecture - or, in casual speech, that you are being deliberately grand for effect.

4. The learned genitive is alive. Unlike the dative, the genitive is a full member of the modern case system, and the learned constructions built on it are productive:

• predicate genitive - a genitive noun phrase as the complement of είμαι: «Είναι της μόδας», «Είμαι της ίδιας γνώμης», «Δεν είναι της προκοπής».
• descriptive / measure genitive - «βιβλίο τριακοσίων σελίδων», «παιδί δέκα ετών», «μιας ώρας δρόμος».
• time genitive - «του χρόνου» (next year), «των Χριστουγέννων», «από Δευτέρας έως Παρασκευής».
• subjective vs objective genitive - «η αγάπη της μητέρας» is ambiguous exactly as English the mother’s love is: she loves (subjective), or she is loved (objective). Greek disambiguates by moving the object out of the genitive: «η αγάπη για τη μητέρα», «η αγάπη προς τη μητέρα».

5. Never mix registers inside one sentence. A καθαρεύουσα connective in the middle of chatty speech is heard as either pompous or ironic - and educated speakers use it for exactly that joke.

Forms & patterns

Dative fossils - learn each as one word

The dative article inside them is fossilised too: τω (masc./neut. sg.), τη (fem. sg.), τοις (masc./neut. pl.), ταις (fem. pl.). Recognise them; never produce new ones.

Adverbial fossils with εκ, εξ, ως, and adverbs in -ως

εξ is simply the form εκ takes before a vowel - it is not an elided word, so it never takes an apostrophe.

The living learned genitive

Subjective against objective genitive

Two full paradigms behind the patterns above

ο χρόνος (time, year) - source of the time genitive «του χρόνου»:

In the meaning “years” the everyday plural is neuter: τα χρόνια, gen. των χρόνων - and the age phrase is «δέκα χρονών».

η άποψη (view, opinion) - a learned feminine in -η / -εις; note the stress shift throughout the plural (άποψη → απόψεις, απόψεων):

With a following weak pronoun the proparoxytone singular takes a second accent: η άποψή μου; the plural απόψεις is paroxytone, so it takes none: οι απόψεις μας.

Register pairs - same meaning, different clothes

The same table read backwards is a joke generator: dropping «ουδέν σχόλιον» or «ως εκ τούτου, αποχωρώ» into a conversation about football is a standard way of sounding mock-solemn, and everyone hears the irony.

Examples

Common mistakes

• εν το μεταξύ -> εν τω μεταξύ - τω is a frozen dative article; the modern το never appears inside this phrase, so store the whole string as one item.
• τις εκατό -> τοις εκατό - τοις is the fossil dative plural article; τις is the modern feminine accusative plural and has nothing to do with percentages.
• εν τη πόλει μας, εν τω σπιτιώ -> στην πόλη μας, στο σπίτι - the dative is dead, so you may quote the surviving phrases but never coin new ones.
• δόξα το Θεό -> δόξα τω Θεώ - “modernising” the cases inside a fossil does not make it more demotic, it just makes it wrong.
• εξ’ αρχής -> εξ αρχής - εξ is the full form of εκ before a vowel, not an elided word, so it takes no apostrophe.
• ούτως ή άλλος -> ούτως ή άλλως - both members are adverbs in -ως; άλλος is the adjective “other” and cannot stand here.
• Όλα εν τάξει; -> Όλα εντάξει; - as the everyday word for “fine, OK” it has fused into a single word; the two-word spelling belongs to formal, legalistic writing.
• Είμαι της άποψη ότι φταίει. -> Είμαι της άποψης ότι φταίει. - the predicate genitive needs a genuinely inflected genitive, not the bare nominative.
• Δεν ήρθα διότι βαριόμουν, ρε συ. -> Δεν ήρθα γιατί βαριόμουν, ρε συ. - one register per sentence; διότι next to ρε συ reads as parody, not as care.

Tips

• Apply the swap test: if you cannot change a single word inside the phrase (*εν τω μικρώ μεταξύ), it is a fossil - file it in your vocabulary notebook, not in your grammar notes.
• Learn each fossil with its spelling and its accents as one block; there is no rule to reconstruct it from, and no rule to protect you if you mis-spell it.
• Fossils are for recognition first. εν τω μεταξύ, εντάξει, τοις εκατό, ούτως ή άλλως and δόξα τω Θεώ are safe to use anywhere; the rest are best kept for writing until you have heard Greeks use them.
• Budget roughly one learned connective per paragraph of speech. Two in a row and you sound like a press release; three and you sound like a comedy sketch - which is precisely why Greeks do it on purpose.
• The productive part of this lesson is the genitive, not the dative. Practise «είμαι της άποψης ότι…», «είναι της μόδας», «βιβλίο διακοσίων σελίδων», «του χρόνου» - these you may build yourself.
• When a genitive could be read two ways, rescue it with για or προς: «η κριτική προς την κυβέρνηση» can only be objective.
• Remember the second accent when a clitic follows a proparoxytone: η άποψή μου, το πρόγραμμά μας, ο δάσκαλός του.