-는-

Etymology
From, representing a merger of two independent  suffixes:  and. It is usually thought that, despite the vowel shift, was closer to the present-tense meaning and that may have been a continuous aspect-marking suffix.

The reduplicated form is used since the seventeenth century, except in certain contexts (see below) where the syncopated form  is used after vowels.

Usage notes

 * This suffix causes stem-final to drop out.
 * This suffix takes the short form after vowels and before the formal non-polite ending . In all other cases, the full form is used:, not , but , not.