In short

English says myself, yourself, each other with dedicated pronouns. Modern Greek has no one-word reflexive pronoun. It uses three different tools instead, and choosing between them is the whole lesson.

• ο εαυτός μου — literally “my self”. ΛΚΝ files εαυτός as a pronoun (αντων.) that declines exactly like an ordinary masculine -ος noun (Ο17, the λαός type), always with the article and a possessive clitic. It stays masculine and singular no matter who the referent is: Η Μαρία μιλάει στον εαυτό της.
• the mediopassive — for things you routinely do to your own body, the voice does the work and no object appears at all: πλένομαι, ντύνομαι, ξυρίζομαι, ετοιμάζομαι.
• ο ένας τον άλλο(ν) and reciprocal mediopassive plurals (αγαπιούνται, φιλιούνται, συναντιόμαστε) — for “each other, one another”; both halves of ο ένας τον άλλο inflect.

Alongside these sits μόνος μου “by myself, on my own”, which agrees with the subject like an -ος, -η, -ο adjective (ΛΚΝ files it in this sense as a determinative pronoun, αντων. οριστ.) — not to be confused with the frozen adverb μόνο “only”.

The rule

1. ο εαυτός μου declines like a noun, so treat it like one. ΛΚΝ classes εαυτός as a pronoun (αντων.) but declines it like an oxytone masculine -ος noun (Ο17, the λαός type). In ordinary syntax it never appears bare: it always carries the definite article and a possessive clitic, and it takes whatever case the verb or preposition assigns — τον εαυτό μου after a transitive verb, στον εαυτό μου after σε, του εαυτού μου as a possessor. Only the clitic tracks the referent. The noun itself is invariably masculine and normally singular, so a woman says τον εαυτό μου, not a feminine form, and a group says τον εαυτό μας, not a plural noun. The plural is not ungrammatical — ΛΚΝ records it precisely when each member of a group is meant separately (Οι μαθητές ζωγράφισαν τους εαυτούς τους) — but the singular is the default, and it is the only safe choice for plain “ourselves”. The article drops in exactly one place, which ΛΚΝ lists apart as λόγια σύνταξη: a few fixed learned phrases after a preposition, αφ’ εαυτού μου / τους “on my / their own initiative” and εκτός εαυτού “beside oneself”.

2. Use εαυτός where the reflexivity is mental, emotional or evaluative. Verbs like ξέρω, προσέχω, εμπιστεύομαι, κατηγορώ, συγκρίνω, βλέπω, ρωτάω take τον εαυτό μου naturally. Use it also after prepositions (για τον εαυτό μου, με τον εαυτό μου, από τον εαυτό μου), where the mediopassive is simply not available.

3. Use the mediopassive for grooming and body care. Where English needs a reflexive pronoun — I wash myself, I get dressed, he shaves — Greek just switches voice. The contrast with the active is exactly the presence of an object: πλένω το παιδί “I wash the child” against πλένομαι “I wash (myself)”. The analytic πλένω τον εαυτό μου is not wrong — ΛΚΝ glosses ντύνω τον εαυτό μου as simply ”= ντύνομαι”, and describes τον εαυτό μου as the object of the unpacked form of a reflexive verb — but it is the marked, emphatic option (Εγώ φροντίζω τον εαυτό μου, κανείς άλλος), so for everyday grooming the voice does the work. The same pairs run through ντύνω / ντύνομαι, ξυρίζω / ξυρίζομαι, ετοιμάζω / ετοιμάζομαι, χτενίζω / χτενίζομαι.

4. μόνος μου agrees; μόνο does not. μόνος, μόνη, μόνο inflects like an ordinary -ος, -η, -ο adjective (ΛΚΝ Ε3), though in this sense the dictionary files it as a determinative pronoun (αντων. οριστ.) and calls it an adjective only in the “sole, only” sense (ο μόνος σκοπός). It agrees with the subject in gender, number and case while the clitic matches the person: μόνος μου, μόνη μου, μόνοι μας, μόνες τους. ΛΚΝ separates three readings, not two: “unaccompanied” (Περπατούσε μόνος του στην παραλία), “unaided” (Λύνει τις ασκήσεις μόνος του) and “of one’s own accord” (Παραδέχτηκε μόνος του το λάθος του, and the phrase από μόνος μου). The adverb μόνο “only” is invariable and never takes a clitic; the two are separated by a single letter, and mixing them is the commonest error in this area.

5. The reciprocal ο ένας τον άλλο(ν) is a two-part frame. The first member is always nominative and agrees with the subject in gender: ο ένας (masculine or mixed), η μία (all female), το ένα (neuter). The second member takes the case the verb or preposition requires and agrees in gender too: τον άλλον, την άλλη, το άλλο; του άλλου, της άλλης; στον άλλον, στην άλλη. The two halves normally straddle the verb: βοηθάνε ο ένας τον άλλον, στηρίζονται ο ένας στον άλλον, διορθώνουν ο ένας τα λάθη του άλλου. A shorter alternative is μεταξύ μας / μεταξύ σας / μεταξύ τους “among ourselves / yourselves / themselves”, which never inflects for gender.

6. Plural mediopassives can be reciprocal on their own. αγαπιούνται “they love each other”, φιλιούνται “they kiss”, συναντιόμαστε “we meet”, τσακώνονται “they quarrel”, αγκαλιάζονται “they hug”, χαιρετιούνται “they greet each other”. Only the plural persons get this reading. Such a verb takes no direct object: the other party either joins the subject (Ο Νίκος και η Άννα συναντιούνται) or comes in με + accusative (Συναντιέμαι με τον Νίκο). Where the plural would be ambiguous between reciprocal and plain passive, add ο ένας τον άλλον to disambiguate.

7. Two productive prefixes. αυτο- builds “self-” nouns (αυτοπεποίθηση, αυτοέλεγχος, αυτοκριτική, αυτοάμυνα) and αλληλο- builds “mutual, each-other” nouns (αλληλογραφία, αλληλεγγύη, αλληλοκατανόηση, αλληλεπίδραση). Both also attach to mediopassive verbs, which is where they replace the constructions above in one word: αυτο- gives reflexives (αυτοκατηγορούμαι = κατηγορώ τον εαυτό μου, αυτοελέγχομαι, αυτοκαταστρέφομαι), αλληλο- gives reciprocals, almost always in the third person plural (αλληλοϋπερασπίζονται, αλληλοενισχύονται, αλληλοεξοντώνονται = υπερασπίζονται / ενισχύονται / εξοντώνονται ο ένας τον άλλον, μεταξύ τους). ΛΚΝ calls αλληλο- a first element of learned origin and tags these verbs «συνήθ. πληθ.», but the pattern is productive rather than a closed list: the dictionary carries dozens of αλληλο- entries and glosses everyday μεταξύ τους sentences with αλληλοαγαπιούνται, αλληλοζηλεύονται, which it does not even list as headwords. The nouns are everyday.

Forms & patterns

εαυτός declined (masculine -ος pattern, ΛΚΝ Ο17)

The vocative survives only in poetic apostrophe (ΛΚΝ tags it ποιητ.), as in αγαπημένε μου εαυτέ!, and ΛΚΝ records the plural only in the oblique cases — the distributive use of rule 1 — so the nominative οι εαυτοί belongs to abstract writing (“selves”), not to ordinary reflexive expression. The stress sits on the last syllable throughout (ΛΚΝ [eaftós], class Ο17), so no second accent is ever needed when the clitic follows.

The reflexive across persons

Every cell keeps ο εαυτός masculine and singular; only the clitic changes.

μόνος, μόνη, μόνο — full declension

Ενικός:

Πληθυντικός:

“By myself” combinations (subject-agreeing μόνος plus person clitic):

άλλος, άλλη, άλλο — full declension

Ενικός:

Πληθυντικός:

ΛΚΝ adds a second set of forms, used especially when άλλος stands on its own without a noun: γεν. ενικού αλλουνού / αλληνής / αλλουνού, γεν. πληθ. αλλωνών, αιτ. πληθ. αλλουνούς (αλλουνού παπά ευαγγέλιο). The frame below uses the regular forms.

The reciprocal frame

Mediopassive reflexives, present tense

Note the stress shift onto the ending in the first person plural: πλένομαι → πλενόμαστε.

Reciprocal mediopassives of contract verbs

The reciprocal reading is available only in the plural persons; the singular forms are plain passives (αγαπιέται “he/she is loved”).

The prefixes αυτο- and αλληλο-

Before a vowel the prefix loses its -ο in older, learned formations (αλληλ- + επίδραση → αλληλεπίδραση; ΛΚΝ admits αλληλοεπίδραση too), while newer coinages keep it. διαλυτικά are then written only where the two vowels would otherwise be read as one digraph — ΛΚΝ spells αλληλοϋπερασπίζομαι and αλληλοϋποβλέπομαι that way — but not in αυτοέλεγχος or αλληλοενισχύονται.

Examples

Common mistakes

• Πλένω τον εαυτό μου κάθε πρωί. -> Πλένομαι κάθε πρωί. — for washing, dressing, shaving and combing, the mediopassive already carries the reflexive meaning; ΛΚΝ records the analytic form only as an equivalent of the mediopassive (ντύνω τον εαυτό μου = ντύνομαι), i.e. as the emphatic option, not as the plain everyday statement.
• Η Μαρία μιλάει στον εαυτό του. -> Η Μαρία μιλάει στον εαυτό της. — εαυτός stays masculine, but the clitic must agree with the real referent.
• Πρέπει να προσέχουμε τους εαυτούς μας. -> Πρέπει να προσέχουμε τον εαυτό μας. — with a plural subject the reflexive normally stays singular; the plural is not wrong, but it says “each of us separately” (ζωγραφίσαμε τους εαυτούς μας), which is rarely what you mean.
• Μιλάει σε εαυτό του. -> Μιλάει στον εαυτό του. — in ordinary syntax εαυτός never appears without the definite article; ΛΚΝ allows the bare form only in the learned fixed phrases αφ’ εαυτού, εκτός εαυτού.
• Οι δύο αδελφές βοηθάνε η μία τον άλλο. -> Οι δύο αδελφές βοηθάνε η μία την άλλη. — both halves of the reciprocal frame agree in gender with the subject.
• Ο ένας βοηθάει ο άλλος. -> Ο ένας βοηθάει τον άλλον. — only the first member is nominative; the second takes the case the verb or preposition demands.
• Στηρίζονται ο ένας τον άλλον σε δύσκολες στιγμές. -> Στηρίζονται ο ένας στον άλλον σε δύσκολες στιγμές. — στηρίζομαι governs σε, so the second member goes into the prepositional phrase, not the bare accusative.
• Συναντιέμαι τον Νίκο κάθε Δευτέρα. -> Συναντιέμαι με τον Νίκο κάθε Δευτέρα. — a reciprocal mediopassive takes no direct object; the other party comes in με + accusative.
• Ο Γιάννης και η Μαρία αγαπιέται. -> Ο Γιάννης και η Μαρία αγαπιούνται. — the reciprocal reading needs a plural subject and a plural verb.
• Πήγα στον γιατρό μόνο. -> Πήγα στον γιατρό μόνος μου. — μόνο is the adverb “only”; “by myself” is the agreeing μόνος with a clitic.
• Είμαστε μόνος μας στο σπίτι. -> Είμαστε μόνοι μας στο σπίτι. — μόνος agrees in gender and number with the subject, and the clitic matches the person.

Tips

• Read ο εαυτός μου literally as “my self”. That one habit predicts everything else: the article is obligatory, the noun is masculine whoever is speaking, it declines through the cases, and it stays singular.
• Divide the work by semantics. Body and grooming → mediopassive (πλένομαι, ντύνομαι, ξυρίζομαι, χτενίζομαι, ετοιμάζομαι). Mind, feelings and judgement → τον εαυτό μου (ξέρω, εμπιστεύομαι, κατηγορώ, συγκρίνω, προσέχω).
• After a preposition the mediopassive is not an option, so εαυτός is the only route: για τον εαυτό μου, με τον εαυτό σου, από τον εαυτό της.
• One-letter test for μόνος / μόνο: if English allows “alone / on my own / by myself”, inflect (μόνος, μόνη, μόνοι, μόνες); if English means “just”, use the frozen μόνο.
• μεταξύ μας is the fastest reciprocal in the language — no gender, no case, just the clitic. Reach for it when ο ένας τον άλλον would clutter the sentence.
• A plural mediopassive can be reciprocal or plain passive (Τα παιδιά χτενίζονται). If context does not settle it, spell it out with ο ένας τον άλλον.
• Treat αυτο- and αλληλο- as vocabulary you can also parse: they build nouns you learn whole (αυτοπεποίθηση, αλληλεγγύη) plus mediopassive verbs that ΛΚΝ tags «συνήθ. πληθ.» (αυτοκατηγορούμαι, αλληλοϋπερασπίζονται). Both prefixes stay productive, so when you meet a new one just read it as “self-” or “one another”.