In short

A normal relative clause hangs off a noun: the book that you brought. A free relative has no noun to hang off - the relative word carries its own head inside it: I’ll bring whatever you want, sit wherever you like, ask whoever is free.

English builds these with the -ever words. Greek builds them with the ό- series:

• όποιος, όποια, όποιο - whoever, whichever (declines like ποιος: -ος, -α, -ο)
• όσος, όση, όσο - as much/many as, all that (declines like a plain adjective: -ος, -η, -ο)
• ό,τι - whatever, what (invariable, written with a comma)
• όπου, όποτε, όπως - wherever, whenever, however/the way that (invariable)
• the emphatic -δήποτε series: οποιοσδήποτε, οτιδήποτε, οπουδήποτε - any at all

Two things carry most of the difficulty, and this lesson is built around them: the spelling contrast ό,τι “whatever” against ότι “that”, and the fact that plain που (lesson 37) cannot start a free relative, because που needs something in front of it.

The rule

1. που needs a head; the ό- words supply their own.

Το βιβλίο που διάβασα - “the book that I read”. Take away το βιβλίο and που is stranded. Greek then has two repairs:

• put in a light head - a demonstrative that means nothing but “the thing/the person”: αυτό που διάβασα, αυτός που ήρθε, εκείνα που είπες·
• use a free relative word, which already contains its head: ό,τι διάβασα, όποιος ήρθε, όσα είπες.

The two are close, but not identical. The light head points at something definite - “the (particular) thing/person”: Αυτός που ήρθε πρώτος κέρδισε = the one who came first won. The bare free relative is free choice and non-specific: Όποιος έρθει πρώτος κερδίζει = whoever comes first wins, no matter who that turns out to be. With ό,τι and αυτό που the difference is often just emphasis, and both are correct.

In the light-head pattern που stays invariable and the demonstrative takes whatever case the main clause demands: Δώσε το σε αυτόν που το ζήτησε.

2. όποιος and όσος decline; ό,τι, όπου, όποτε, όπως do not.

όποιος and όσος are ordinary three-ending nominals - όποιος takes the -ος, -α, -ο endings of ποιος, όσος the -ος, -η, -ο endings of a plain adjective: they agree in gender, number and case, and όσος also agrees with a following noun (όσα βιβλία, όσες καρέκλες). ό,τι, όπου, όποτε and όπως never change shape.

3. Case: the pronoun takes the case of the job it is doing.

A free relative word stands in two clauses at once, so two things can claim its case: its job inside the relative clause, and its job in the main clause. Often they agree and there is nothing to decide:

• Δώσε το σε όποιον θέλεις. - σε wants the accusative, and θέλεις wants an accusative object too. Both point the same way: όποιον.
• Όποιος τελειώσει νωρίς, ας περιμένει έξω. - subject of τελειώσει and subject of the whole sentence: nominative both times.
• Όποιον καλέσεις θα έρθει. - here the embedded verb decides: καλέσεις takes an accusative object, so όποιον, even though the phrase is the subject of θα έρθει.

When the two clash, the nominative is what gives way: an accusative demanded by a preposition or by a transitive verb - in either clause - fixes the form. Grammars call this έλξη, “attraction”:

• Μίλησε με όποιον ήρθε. - ήρθε on its own would give the nominative όποιος, but με imposes the accusative: όποιον.
• Βοήθησε όποιον σε χρειάζεται. - subject of χρειάζεται, yet object of βοήθησε, and the object case wins.

Attraction has a condition, and the ΛΚΝ spells it out: the pronoun takes the case of the demonstrative that has been left out - για όσους ρώτησαν is για εκείνους όσοι ρώτησαν with the εκείνους dropped. Put a head back in front and there is nothing left to attract to, so the relative keeps its own case: Πλήρωσε όλους όσοι δούλεψαν εκείνη τη βδομάδα - accusative όλους, nominative όσοι.

The practical lesson for a learner is the opposite of the English habit: when it stands bare, never leave όποιος/όσος in the nominative just because it is followed by a verb. Look at the preposition or the verb it sits next to in the main clause first.

4. ό,τι against ότι. Both are made of the same sounds, and the comma (η υποδιαστολή) is the only signal you can spell by; it is obligatory. (The one difference the dictionary records is prosodic, not segmental: ΛΚΝ transcribes the pronoun stressed, [óti], and the conjunction unstressed, [oti] - the same treatment it gives πώς [pós] against πως [pos]. That is a fact about sentence rhythm, not something you can hear word by word.) ό,τι is the free relative “whatever, what”; ότι is the conjunction “that” that opens a complement clause after λέω, νομίζω, ξέρω, ελπίζω (lesson 36). Full discrimination table below.

Two neighbours are left for later: the inflected written relative ο οποίος belongs to lesson 58, and the concessive όποιος / ό,τι κι αν (“whoever/whatever may…”) to lesson 47.

Forms & patterns

όποιος, όποια, όποιο - whoever, whichever, any that. The same endings as ποιος, but not the same stress: ΛΚΝ files όποιος under inflection class Ε4 (stem-stressed -ος, -α, -ο, like άδειος) and ποιος itself under Ε2 (end-stressed -ός, -ά, -ό).

Pronouns have no vocative: you cannot call out to “whoever”, so those cells stay empty. The accent never moves off the ο- in any cell of this table. Beside it the dictionary records a second, spoken genitive, used mainly when the pronoun stands on its own - οποιανού, οποιανής, οποιανού, and (rare) plural οποιανών - and there the stress does move; the forms in the table are the ones to write.

όσος, όση, όσο - as much as, as many as, all that. Plain -ος, -η, -ο endings (ΛΚΝ class Ε3, the ordinary adjective class of αεράτος, αγριεμένος).

The masculine accusative singular of όσος is όσο, with no final -ν: here όσος behaves like a plain adjective (the -ν survives only in fossilised λόγιες phrases such as όσον αφορά). όποιον, by contrast, patterns with the pronouns αυτόν and τον and keeps its -ν when it stands on its own; in front of a noun it follows the ordinary final-ν rule of lesson 8 - όποιον τρόπο κι αν διαλέξεις, but όποιο δρόμο κι αν πάρεις.

The invariables. These never change for gender, number or case. Standing on its own, ό,τι is a neuter singular, and ΛΚΝ restricts it to the nominative and the accusative - there is no genitive of it. In front of a noun, though, it imposes nothing: the noun may be of any gender and number - ό,τι μέρα προτιμάς, ό,τι φίλο συναντήσεις, ό,τι ρούχα φοράς.

The -δήποτε series - “any … at all”. One word, one accent, on -δή-, and no comma anywhere. Of the forms below only οποιοσδήποτε declines, and it declines in its first half. The series has one further declining member that the tables leave out: ΛΚΝ also lists οσοσδήποτε, οσηδήποτε, οσοδήποτε “however much/many”, the -δήποτε of όσος, declined on the same Ε3 pattern - οσεσδήποτε ώρες κι αν δουλέψεις, δε θα προλάβεις.

ό,τι against ότι - the discrimination table.

Bare free relative against light head. Both are grammatical; the right-hand column is more definite and more specific.

Examples

Common mistakes

• Γράψε που σου λέω. -> Γράψε ό,τι σου λέω. - που must have a noun in front of it; with nothing to attach to you need ό,τι or the light head αυτό που.
• Αυτό ό,τι μου είπες με στενοχώρησε. -> Αυτό που μου είπες με στενοχώρησε. - once you supply a head (αυτό), the relative word is που; ό,τι already carries its own head and cannot take a second one.
• Μου είπε ό,τι θα αργήσει. -> Μου είπε ότι θα αργήσει. - “that” after a verb of saying is ότι without a comma; the comma spelling would mean “whatever”.
• Κάνε ότι θέλεις. -> Κάνε ό,τι θέλεις. - here the word is the object of θέλεις (“whatever”), so it takes the υποδιαστολή.
• Ρώτησε ποιον εμπιστεύεσαι. -> Ρώτησε όποιον εμπιστεύεσαι. - ποιος only asks a question; the free relative adds the ό-.
• Δώσε το σε όποιος θέλεις. -> Δώσε το σε όποιον θέλεις. - όποιος declines like αυτός, and after σε it must be accusative, whatever follows it.
• Πήρα όσο βιβλία ήθελα. -> Πήρα όσα βιβλία ήθελα. - όσος agrees with its noun in gender, number and case, exactly like an adjective.
• Πήγαινε πού θέλεις. -> Πήγαινε όπου θέλεις. - accented πού only asks “where?”; the free relative is όπου.
• Θα φέρω ό,τιδήποτε θέλεις. -> Θα φέρω οτιδήποτε θέλεις. - the comma belongs to ό,τι alone; οτιδήποτε is one unbroken word with a single accent on -δή-.
• Θα το κάνω οπωσδήποτε θέλεις. -> Θα το κάνω όπως θέλεις. - οπωσδήποτε does not mean “in any way at all”; it means “definitely, without fail”.

Tips

• The comma test, in two seconds: if οτιδήποτε or αυτό που fits, write ό,τι; if πως fits, write ότι. Nothing else decides it: the two are made of the same sounds, and the only difference the dictionary records - stressed ό,τι against unstressed ότι, exactly as with πώς against πως - lives in the sentence rhythm and is not something you can count on hearing.
• Keep the minimal pair in your ear: Κάνε ό,τι θέλεις “do whatever you want” against Κάνει ότι δεν ακούει “he pretends (that) he isn’t listening”.
• Whenever you write όποιος or όσος, look left before you choose the ending: a preposition (σε, με, από, για) or a transitive verb in the main clause will pull it into the accusative even though a verb follows it.
• Learn the ό- words as a family against their question-word twins: πού; / όπου, πώς; / όπως, πότε; / όποτε, ποιος; / όποιος. Only πού and πώς need the disambiguating accent; πότε is accented like any other polysyllable and ποιος, being one syllable, takes none.
• Do not confuse όποτε “whenever” with οπότε “so, and then” - different accent, different word: Ξεκίνα όποτε είσαι έτοιμος vs Άργησε, οπότε φύγαμε.
• The -δήποτε words add “at all, it makes no difference”: οποιοσδήποτε γιατρός “any doctor at all”. They are one word, one accent, no comma, and of the ones above only οποιοσδήποτε changes shape - the dictionary adds one more that does, οσοσδήποτε.
• Remember the second accent when a weak pronoun leans on a word stressed three syllables back: Δώσε τα πράγματά μου σε όποιον τα ζητήσει. Μαγείρεψέ το όπως θέλεις.