" When today we say ‘form’, we mean only the visible and measurable aspects of a thing, especially its spatial contours. For the Medieval masters, on the other hand…’form’ was the sum total of the essential properties or qualities of a thing; it was what constituted the inner unity of a manifested object. ‘The forms of things,’ writes Thierry of Chartres, ‘are outside and beyond matter, contained in the Divine Spirit. There, in its simple and immutable fullness, true forms exist. But those which, in a certain and not fully explicable way, are impregnated into matter, are so to speak ephemeral and not forms in the true sense. They are only something like the reflections or representations of true forms.
True form is thus neither limitable nor mutable; it is like a ray of the creative Spirit which, descending into matter, fleetingly lends it form. An analogy for this is artistic creation: just as the artist may more or less completely...imprint on a material the spiritual picture that he carries within himself, so the essence of a thing may manifest itself more or less perfectly in that particular thing. "

― Titus Burckhardt , Chartres And The Birth Of The Cathedral