How are the adjectives conjugated to izenkei (うれしけれ, たのしけれ) used here?


I came across a "Mermaid's song" in a text:

> ものみな眠るさ夜なかに  
>  水底を離るることぞ **うれしけれ** 。  
>  水のおもてを頭もて、  
>  波立て遊ぶぞ **たのしけれ** 。  
>  澄める大気をふるわせて、  
>  互に高く呼びかわし  
>  緑なす濡れ髪うちふるい、  
>  乾かし遊ぶぞ **たのしけれ** ！

The bolded adjectives, うれし（い）、たのし（い）、both seem to be [conjugated to
izenkei](http://www.weblio.jp/content/%E5%AC%89%E3%81%97%E3%81%91%E3%82%8C).
If that is so, can izenkei of shiku adjectives be used in exclamatory
function? E.g. second line as "how happy (I) am to leave the depths!".

If it's not exclamatory, then what could it it mean here? And if it's not
izenkei, then what else is it?




In classical Japanese, **"～ぞ + 連体形"** and **"～こそ + 已然形"** are the patterns
which basically emphasize the sentences. This grammatical rule is known as
[係り結び](http://manapedia.jp/text/345). To put it simply, when ～ぞ or ～こそ appears
in the middle of a sentence, that sentence have to end with 連体形 or 已然形 (of a
verb/adjective), respectively.

>   * 雪降りけり。 (終止形)
>   * 雪ぞ降りける。 (ぞ + 連体形)
>   * 雪こそ降りけれ。 (こそ + 已然形)
>   * 雪が降った。 (modern Japanese)
>

However, the lyrics in this song doesn't seem to follow the general rule, in
that ～ぞ is followed by 已然形. I think it should be either "水底を離るることぞうれしかる" or
"水底を離るることこそうれしけれ".

But my knowledge on classical Japanese is very limited, so I'd like to hear
opinions from others.




In classical Japanese, **"～ぞ + 連体形"** and **"～こそ + 已然形"** are the patterns
which basically emphasize the sentences. This grammatical rule is known as
[係り結び](http://manapedia.jp/text/345). To put it simply, when ～ぞ or ～こそ appears
in the middle of a sentence, that sentence have to end with 連体形 or 已然形 (of a
verb/adjective), respectively.

>   * 雪降りけり。 (終止形)
>   * 雪ぞ降りける。 (ぞ + 連体形)
>   * 雪こそ降りけれ。 (こそ + 已然形)
>   * 雪が降った。 (modern Japanese)
>

However, the lyrics in this song doesn't seem to follow the general rule, in
that ～ぞ is followed by 已然形. I think it should be either "水底を離るることぞうれしかる" or
"水底を離るることこそうれしけれ".

But my knowledge on classical Japanese is very limited, so I'd like to hear
opinions from others.

