Unrealistic hopes (7,2,3,3)
I believe the answer is:
castles in the air
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">unrealistic hopes</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for castles in the air that I've seen before include "rooks circling overhead" , "Fancies" , "Unrealistic hopes" , "daydreams" , "dreamy schemes" .)