-ся

• -сь (-sʹ) (after vowels)

From Old East Slavic сѧ (sę), from Proto-Slavic *sę. It is considered the shortened form of себя́ (sebjá).

• IPA^(key): [sʲə]
• IPA^(key): [sə] (after т or ть, see usage notes)

-ся • (-sja)

1. Reflexive suffix appended to finite verbs and infinitives to make a reflexive, reciprocal, intransitive or passive verb.

• After a vowel, -ся is usually contracted to -сь, except when attached to an adjectival participle:
  • мы́ться (mýtʹsja, “to wash oneself”), мо́ется (mójetsja, “[he] washes himself”)
  • мо́юсь (mójusʹ, “[I] wash myself”)
  • мы́вшаяся (mývšajasja, “having been washing herself”).
• When affixed to an infinitive -ть (-tʹ) or the 3rd-person singular or plural -т (-t), it merges with the /tʲ/ or /t/ into the affricate /ts/ and palatalization is lost: [tsə].