all slavsh verbs have -иь.

"to see" - сиь (si')

"i see" - я си (ya si)

"i saw" - я сат (ya sat)

there is also no "have [verb]", as in "have seen", so "I have seen" is also "ya sat".

Учиь (uchi') - to learn

я учи (ya uchi) - i learn

я учат (ya uchat) - i learned, have learned