Complex sentence: Kant's "Copernican revolution" was the inversion of the traditional relation between the subject of knowledge and the object of that knowledge: instead of the observed objects affecting the observing subject, the subject's constitution affects the way that the objects are observed.
Split into simpler sentences: Kant's "Copernican revolution" was the inversion of the traditional relation between the subject of knowledge and the object of that knowledge. Instead of the observed objects affecting the observing subject, the subject's constitution affects the way that the objects are observed.