How to use じゃ in grammar?

Question

Apart from the standard じゃね, じゃまた and それじゃ (In the "I'm heading off" sense) for the different variations of goodbye, and じゃ as an informal inflection of では for 'is not' for じゃない, I have no idea how to use it.

I've seen it in some song lyrics like 「見ているだけじゃ始まらない」, 「足踏みしてるだけじゃ進まない」 and 「それだけじゃお腹がすくわ」.

I notice it seems like a conditional form. Why can't it be "Miteiru dake nara hajimaranai?" and "Ashibumishiteru nara susumanai"?

I also noticed all of them have a dake preceding the じゃ. So is this a special grammar pattern of "だけじゃ"? I almost thought that the following verb is always negative like the classic "Ja Nai" except for the fact that this set of lyrics 「それだけじゃお腹がすくわ」 breaks that theory of mine.

Answer 1

Basically, じゃ is the informal form of では. It can be used in two ways:

1. で+は (locative particle + topic particle) to indicate the location as the topic of the sentence.

• ここではVRゲームができます。(VR Games can be played HERE.)

2. では (conjunction) "then"

• 見ているだけじゃ始まらない。 (Just looking then nothing will start.)

だけ means "just", may imply "not enough" in some contexts.

Reference 1, Reference 2