-ся (зворотне значення)

The reflexive marker in Ukrainian is a postfix, meaning it follows all other suffixes and endings. Historically, it is a shortened form of the reflexive pronoun себе (oneself). Its form generally changes based on the sound immediately preceding it to maintain euphony (милозвучність):

• -ся: The standard form used after consonants (e.g., вмиваються, миється). It is also the fixed literary standard for the first and second person plural endings -емося and -етеся (e.g., вмиваємося), where the -сь variant is considered colloquial or poetic.
• -сь: The standard form used after vowels (e.g., миюсь, вмивалася). While -ся can sometimes be used after a vowel as a stylistic choice to avoid a difficult consonant cluster in the following word, -сь is the default grammatical preference. At the absolute end of a sentence, both are acceptable after a vowel, though -сь remains more common.
• Morphological Exception: Adverbial participles almost exclusively take the -сь form regardless of the following sound (e.g., дивлячись, сміючись, вмившись).

Pronunciation Note: When -ся attaches to certain verb endings, the sounds merge. The ending -ться is pronounced as [ц':а] (a long soft 'ts' sound followed by 'a'), and -шся is pronounced as [с':а] (a long soft 's' sound followed by 'a'). In imperative forms, -жся is pronounced as [з'с'а] (e.g., ріжся) and -чся is pronounced as [ц'с'а] (e.g., не морочся).

In the infinitive, both -тися and -тись are standard and grammatically correct (e.g., вмиватися or вмиватись), though -тися is used as the dictionary form.

Key Functions:
1. Self-Directed Action: The subject and the object are the same. For example, мити (to wash something) becomes митися (to wash oneself).
2. Reciprocal Action: Indicates mutual action between two or more subjects (e.g., зустрічатися — to meet each other, обійматися — to hug each other).
3. Subject Characteristic: Describes a permanent property, tendency, or ability of the subject (e.g., собака кусається — the dog bites, скло б'ється — glass breaks).
4. Transitivity Shift: Adding the postfix makes the verb strictly intransitive, meaning it grammatically cannot take a direct object in the accusative case without a preposition.
5. Impersonal Meanings: Expresses states or feelings without a clear subject (e.g., Мені не спиться — I can't sleep).
6. General Intransitive (Middle Voice): Describes a change of state or internal process where the subject is affected, such as хвилюватися (to worry) or прокинутися (to wake up).
7. Intensive-Resultative (Cumulative): Often used with the prefix на- to indicate performing an action to the point of full satisfaction or exhaustion (e.g., наїстися — to eat one's fill, напрацюватися — to work oneself to exhaustion).
8. Indirect Reflexive: The action is performed for one's own benefit (e.g., запасатися — to stock up, збиратися — to get ready).
9. Middle-Passive: Describes actions happening automatically or generally, without specifying an agent (e.g., Двері відчиняються автоматично — The doors open automatically, Як це пишеться? — How is this written?).

Important Stylistic Note: While -ся was historically used for the agentive passive voice, this is often avoided in modern standard Ukrainian in favor of active constructions or impersonal forms. However, subjectless middle-passive constructions (like Книга добре продається) are completely natural and correct.

Note that -ся can also be a required part of reflexive-only verbs. These verbs only exist with the -ся postfix and have no non-reflexive counterpart. Examples include сміятися (to laugh), сподіватися (to hope), пишатися (to be proud), and боятися (to fear).