?????? ?? ?? ?? ???? ???????????? ??????????The 2 most commonly encountered grammatical rules in which this occurs is when conjugating previously or existing tenses. For examples:???? ?????????????? ????, ?? ?? ?? ???? ??? ????? ?????????????? ??????(??)???? ???????? ???? ??????, ???? ???, ???? ?? ?? ?? ????????????????? /??/ ??  ???? ? ?? ?? ?? ?