Full Idea
Although it might be right to say that imagination is required in order to make reasoning and understanding possible, this also works the other way, as imagination cannot occur without some prior understanding.
Gist of Idea
Understanding is needed for imagination, just as much as the other way around
Source
Alex Betteridge (talk [2005]), quoted by PG - Db (ideas)
A Reaction
This strikes me as a very illuminating remark, particularly for anyone who aspires to draw a simplified flowdiagram of the mind showing logical priority between its various parts. In fact, the parts are interdependent. Maybe imagination is understanding.