What then is truth? 

A movable host of metaphors, metonymies, and anthropomorphisms:

 in short, a sum of human relations which have been poetically and rhetorically intensified, transferred, and embellished, and which, after long usage, seem to a people to be fixed, canonical, and binding. 

Truths are illusions which we have forgotten are illusions 

— they are metaphors that have become worn out and have been drained of sensuous force.