The rhythm of relations of color and size makes the absolute appear in the relativity of time and space. - Piet Mondrian

the Cubists in Paris made me see that there was also a possibility of suppressing the natural aspect of form. I continued my research by abstracting the form and purifying the colour more and more. While working, I arrived at suppressing the closed effect of abstract form, expressing myself exclusively by means of the straight line in rectangular opposition; thus by rectangular planes of colour with white, grey and black. At that time, I encountered artists with approximately the same spirit, First Van der Leck, who, though still figurative, painted in compact planes of pure colour. My more or less cubist technique - in consequence still more or less picturesque - underwent the influence of his exact technique. Shortly afterwards I had the pleasure of making the acquaintance of Van Doesburg. Full of vitality and zeal for the already international movement that was called 'abstract', and most sincerely appreciative of my work, he came to ask me to collaborate in a review he intended to publish, and which he [Theo van Doesburg] was to call 'De Stijl'. I was happy with an opportunity to publish my ideas on art, which I was engaged in writing down: I saw the possibility of contacts with similar efforts.

Vertical and horizontal lines are the expression of two opposing forces; they exist everywhere and dominate everything; their reciprocal action constitutes 'life'. I recognized that the equilibrium of any particular aspect of nature rests on the equivalence of its opposites.

Dear Does [= Theo van Doesburg ], thank you for your letter.. .I was glad to know that in principle you are in favour of the diamond hanging [Mondrian's painting, he made in 1919, hanging in a rhombus] and I think that in practice you will approve of this method for some of my things. You look at the thing [painting] itself, and not only the outward appearance..