Full Idea
It does not follow that what we can't imagine does not exist.
Gist of Idea
What we cannot imagine may still exist
Source
Gottfried Leibniz (Letters to Johann Bernoulli [1699], 1698.11.18)
Book Reference
Leibniz,Gottfried: 'Philosophical Essays', ed/tr. Arlew,R /Garber,D [Hackett 1989], p.168
A Reaction
This just establishes the common sense end of the debate - that you cannot just use your imagination as the final authority on what exists, or what is possible.