Full Idea
The light dove, in free flight cutting through the air the resistance of which it feels, could get the idea that it could do even better in airless space. ..Plato made no headway in the empty space of understanding; he had no resistance, no support.
Gist of Idea
A dove cutting through the air, might think it could fly better in airless space (which Plato attempted)
Source
Immanuel Kant (Critique of Pure Reason [1781], B008/A5)
Book Reference
Kant,Immanuel: 'Critique of Pure Reason', ed/tr. Guyer,P /Wood,A W [CUO 1998], p.140
A Reaction
Who says Kant can't write? This is the classic image of the excesses of metaphysics which Kant wished to curtail. His attacks culminates in the contempt of logical positivism for such things, but no one would now disagree with Kant on this.