[2] Wölfflin tentatively offered several alternative pairs of terms, in particular "a-tectonic" and "tectonic" (also free/strict and irregular/regular), but settled on open/closed because, despite their undesirable ambiguity, they make a better distinction between the two styles precisely because of their generality.
[3] In general, the closed compositions of the 16th century are dominated by the vertical and horizontal, and by the opposition of these two dimensions.
Seventeenth-century painters, by contrast, de-emphasize these oppositions so that, even when they are present, they lose their tectonic force.
The diagonal, on the other hand, becomes the main device used to negate or obscure the rectangularity of the picture space.
The others were the linear and the painterly, plane and depth, multiplicity and unity, and clearness and unclearness.