??? ?????? ????????? ???? ?????????? ????The 2 most popular grammatical principles where by this occurs is when conjugating before or existing tenses. For illustrations:???? ????? ???? ???? ???????? ??????????????- ???? ?????????? ???? ???????? ?????????? ??????????? ????????.????????, ???????? ?? '?????? ?? ???? ??? ?????? ?? ?? ????.?? ?? ??????