Mondrian sets forth the delimitations of Neoplasticism in his essay "Neo-Plasticism in Pictorial Art". He writes, "this new plastic idea will ignore the particulars of appearance, that is to say, natural form and colour. On the contrary, it should find its expression in the abstraction of form and colour, that is to say, in the straight line and the clearly defined primary colour". With these constraints, his art allows only primary colours and non-colours, only squares and rectangles, only straight and horizontal or vertical lines. The De Stijl movement posited the fundamental principle of the geometry of the straight line, the square, and the rectangle, combined with a strong asymmetricality; the predominant use of pure primary colors with black and white; and the relationship between positive and negative elements in an arrangement of non-objective forms and lines.