-ся/-сь (прошедшее время)

Reflexive verbs in Russian are formed by adding the reflexive postfix to the very end of the verb. In the past tense, this postfix usually follows the standard gender and plural endings.

1. The Spelling Rule:

• -ся is used after consonants. While this most often follows the masculine ending -л (e.g., оделся - he dressed himself), it also applies to masculine verbs where the -л is dropped after a consonant stem, such as some verbs ending in -ти (e.g., спастись -> спасся), -чь (e.g., обжечься -> обжёгся), -ереть (e.g., запереться -> заперся), and some others (e.g., ошибиться -> ошибся). Note that in the feminine, neuter, and plural forms of these verbs, the -л returns, and they follow the vowel rule, taking -сь (e.g., спаслась, спаслись).
• -сь is used after vowels. This occurs in the feminine (-ла), neuter (-ло), and plural (-ли) forms (e.g., оделась - she dressed herself, оделись - they dressed themselves).

Note: Adjectival participles are an exception to this rule and always take -ся even after vowels (e.g., одевшаяся). For adverbial participles (gerunds) in the past tense, the standard non-reflexive suffix -в (e.g., одев) is replaced by the alternative suffix -вши specifically so that the reflexive -сь can be attached (resulting in одевшись).

2. Pronunciation:
Unlike the infinitive (-ться) and 3rd person forms (-тся) where the reflexive ending is pronounced as a hard [ц:а], the past tense -ся (e.g., in -лся) has a soft consonant [с']. Because this ending is usually unstressed, the vowel reduces, sounding more like [с'ь] or [с'ə] (e.g., оделся). It is only pronounced with a full [а] sound when stressed (e.g., родился).

3. The Rule of Intransitivity:
Adding -ся/-сь generally makes a transitive verb intransitive. A reflexive verb almost never takes a direct object in the Accusative case without a preposition, though there are a few exceptions (e.g., слушаться маму - to obey mom).

4. Common Functions:

• Direct Reflexive: The subject performs the action on themselves (e.g., умылся - he washed himself).
• Reciprocal: Multiple subjects perform the action on each other (e.g., встретились - they met each other).
• Inherent: Verbs that are always reflexive (e.g., смеялся - he laughed, боялся - he was afraid).
• Emotions and Spontaneous Actions: Many verbs describing feelings are reflexive (e.g., радовался - he was glad). Reflexive verbs are also used for spontaneous actions or changes of state where an action happens without a specified agent (e.g., дверь открылась - the door opened, чашка разбилась - the cup broke).
• Passive Voice: Used with imperfective verbs to show an action being done to the subject (typically restricted to inanimate subjects; e.g., дом строился - the house was being built).
• Impersonal: Used without a nominative subject to describe states or spontaneous actions. The verb is always in the neuter form -лось. When there is an experiencer, it is in the Dative case (e.g., мне не спалось - I couldn't sleep, нам хотелось - we wanted to), but many impersonal reflexives take no experiencer at all (e.g., оказалось - it turned out).
• Characteristic: Describes a typical behavior or property of the subject (e.g., собака кусалась - the dog used to bite).

5. Stress Shifts:
Be aware that in the past tense of some reflexive verbs, the stress shifts to the reflexive postfix or the feminine ending, contrasting with the base verb (e.g., нАчал vs. началсЯ; взял vs. взялсЯ). In the feminine form, the stress often falls on the ending (e.g., началАсь, взялАсь).

6. Word Order and Negation:
The postfix always remains attached to the end of the verb form. To negate the action, place не before the verb as usual.