As you can see this is a composition of vertical and horizontal lines which will (in an abstract manner) have to express the idea of rising upwards, … - Piet Mondrian

[the double line in his paintings] is still one line, as in the case of your grooves [= the wide sunken lines in the relief's, the artist Gorin made then].. .In my last things the double line widens to form a plane, and yet it remains a line. Be that as it may, I believe that this question is one of those which lie beyond the realm of theory, and which are of such subtlety that they are rooted in the mystery of 'art'. But all that is not yet clear in my mind.

Gradually I became aware [c. 1914-1918] that Cubism did not accept the logical consequences of its own discoveries; it was not developing abstraction towards its ultimate goal: the expression of pure reality.

If, then, we focus our attention on the balanced relation, we shall be able to see unity in natural things. However, there it appears under a veil. But even though we never find unity expressed exactly, we can unify every representation, in other words, the exact representation of unity can be expressed; it must be expressed, for it is not visible in concrete reality.