grammar - 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?

Answer

～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")