What's the い in ない?


I've heard that the non-past negative form ends in nai. However, other forms
will aswell have na alone (na katta). Is there some meaning behind this い or
is that how the form is?




In Standard Japanese, the negative particle (auxiliary) has been totally
conflated with the adjective ない "not exist" in form. And in older language,
the form corresponds to ない was なき (naki), so it was sharing the last _-k_ with
other forms. It seems somewhat irregular only after the _k_ -sound dropped
before _i_. Some dialects drop _k_ before other vowels, which makes
conjugation more complex (See
[1](https://japanese.stackexchange.com/q/24217/7810),
[2](https://japanese.stackexchange.com/q/42890/7810)). It is not uncommon that
velar consonants disappear in the middle of word.

> English _sail_ < Old English _segel, segl_ (cf. German _Segel_ )  
>  English _royal_ < French _royal_ < Latin _regalis_

By the way, the perfect (past) form なかった (nakatta) is originally a contraction
of なく (naku) + あった (atta "was").




In Standard Japanese, the negative particle (auxiliary) has been totally
conflated with the adjective ない "not exist" in form. And in older language,
the form corresponds to ない was なき (naki), so it was sharing the last _-k_ with
other forms. It seems somewhat irregular only after the _k_ -sound dropped
before _i_. Some dialects drop _k_ before other vowels, which makes
conjugation more complex (See
[1](https://japanese.stackexchange.com/q/24217/7810),
[2](https://japanese.stackexchange.com/q/42890/7810)). It is not uncommon that
velar consonants disappear in the middle of word.

> English _sail_ < Old English _segel, segl_ (cf. German _Segel_ )  
>  English _royal_ < French _royal_ < Latin _regalis_

By the way, the perfect (past) form なかった (nakatta) is originally a contraction
of なく (naku) + あった (atta "was").

