Even space and time, as pure as these concepts are from everything empirical and as certain as it is that they are represented in the mind completely a priori, would still be without objective validity and without sense and significance if their necessary use on the objects of experience were not shown; indeed, their representation is a mere schema, which is always related to the reproductive imagination that calls forth the objects of experience, without which they would have no significance; and thus it is with all concepts without distinction.