What is the difference between ずに and ない-form?


My wife is studying for the JLPT exam, and came across the following question:

> ２時間、＿＿＿＿＿立って話しました。

She narrowed the choices down to:

  1. すわらずに
  2. すわらないと

Or another similar question:

> あの花は５日に＿＿＿＿＿とさきません。

  1. ならず
  2. ならない

In both cases, the two answers seem "correct". According to the answers 1 is
correct is both cases, but many people suggested number 2 seems better.  
What is the difference between ずに and ない-form? Why would the ない-form be wrong
here?




～ず and ～ない mean essentially the same thing, as they are both negative forms
(i.e. they both mean "not"). ず is more of a written or formal style, while ない
is spoken or standard.

However, the examples in your question actually revolve around ～に and ～と, as
it's a grammar usage question. Let's take a look at your examples:

> ２時間、＿＿＿＿＿立って話しました。

座【すわ】らずに is the correct answer here, and has several close analogues that
could be used as well:

  * 座【すわ】らなくて
  * 座【すわ】らないで
  * 座【すわ】ることなく

The nuances may vary slightly between these, but they all fit in the sentence
grammatically, which is what these questions are designed to test.

> あの花は５月に＿＿＿＿＿とさきません。

In this example, the time (5月に) is the hint and the key is the と after the
blank. Though ～ず can be followed by と, it ends up having the same meaning as
～ずに, so the answer has to be ならない, as ～ないと deals with time.

**But why?**

Though the meanings of ～ず and ～ない are basically the same, the meanings diverge
when they become ～ずに and ～ないと.

  * ～ずに means basically "without doing ～" (～に just turns this into an adverb, just like the で in ～ないで)
  * ～ないと on the other hand, means "when not doing ～" or "if [it] doesn't ～" (～と in this case means "when" or "if")




～ず and ～ない mean essentially the same thing, as they are both negative forms
(i.e. they both mean "not"). ず is more of a written or formal style, while ない
is spoken or standard.

However, the examples in your question actually revolve around ～に and ～と, as
it's a grammar usage question. Let's take a look at your examples:

> ２時間、＿＿＿＿＿立って話しました。

座【すわ】らずに is the correct answer here, and has several close analogues that
could be used as well:

  * 座【すわ】らなくて
  * 座【すわ】らないで
  * 座【すわ】ることなく

The nuances may vary slightly between these, but they all fit in the sentence
grammatically, which is what these questions are designed to test.

> あの花は５月に＿＿＿＿＿とさきません。

In this example, the time (5月に) is the hint and the key is the と after the
blank. Though ～ず can be followed by と, it ends up having the same meaning as
～ずに, so the answer has to be ならない, as ～ないと deals with time.

**But why?**

Though the meanings of ～ず and ～ない are basically the same, the meanings diverge
when they become ～ずに and ～ないと.

  * ～ずに means basically "without doing ～" (～に just turns this into an adverb, just like the で in ～ないで)
  * ～ないと on the other hand, means "when not doing ～" or "if [it] doesn't ～" (～と in this case means "when" or "if")

