Grammatical justification for でしかない


The song [eX
Dream](http://tw.myblog.yahoo.com/cathy910732/article?mid=1128&prev=1129&next=382&page=1)
by Myuji (which appears [in an anime
OP](http://en.wikipedia.org/wiki/List_of_X_episodes)) contains the sentence:

> [夢]{ゆめ}は夢でしかない

The general point of the sentence is fairly clear, meaning "a dream is just a
dream". But what is the best way to think of the でしかない construction?

At first I saw it as 夢は夢で, as in, "a dream is a dream and...", but now I'm
wondering how correct this is or if it's correct at all.

Is it better to look at it as a separation of the parts of である? Does this
happen in many other cases, where you use a qualified で followed by ある?




Let's start with something common:

> 夢は夢だ。 'Dreams are dreams.'

Let's negate it (using ではない instead of its contracted form じゃない):

> 夢は夢ではない。 'Dreams are not dreams.'

は is a 係助詞{かかりじょし} ("binding particle"). Any 係助詞 fits in this spot. しか is also
a 係助詞:

> 夢は夢でしかない。'Dreams are nothing but dreams.'

* * *

The "modern" grammatical analysis of this stuff is that で is the 連用形{れんようけい}
("continuative form") of the copula だ which results in ではない and でしかない falling
nicely into this general rule:

> (連用形 of something) + (optional 係助詞) + (ない or ある)

Some other instances of this rule are `すごく（は）ない`、`あつく（も）ない`、`バカで（も）ある`。




Let's start with something common:

> 夢は夢だ。 'Dreams are dreams.'

Let's negate it (using ではない instead of its contracted form じゃない):

> 夢は夢ではない。 'Dreams are not dreams.'

は is a 係助詞{かかりじょし} ("binding particle"). Any 係助詞 fits in this spot. しか is also
a 係助詞:

> 夢は夢でしかない。'Dreams are nothing but dreams.'

* * *

The "modern" grammatical analysis of this stuff is that で is the 連用形{れんようけい}
("continuative form") of the copula だ which results in ではない and でしかない falling
nicely into this general rule:

> (連用形 of something) + (optional 係助詞) + (ない or ある)

Some other instances of this rule are `すごく（は）ない`、`あつく（も）ない`、`バカで（も）ある`。

