This is not meant to say that knowledge does not correspond to objective reality. On the contrary, it is believed that reality as it is in itself can in principle be known.
But the way of expressing our knowledge, for example predication, does not necessarily correspond to objective reality, in the sense that the structure of our expressions does not necessarily correspond with the structure of objective reality. The structure of predication, for example, consists in a coupling of subject and predicate. As such it suggests a corresponding coupling of substrate and carried content. But this does not necessarily need to be so. When we say ' crystals are periodic ' we can verify the truth of this proposition by investigating many crystals by means of the X-ray diffraction method. But such a verification does not necessarily mean that for every given crystal we have a substrate which carries the content periodic.