In contrast to this alteration, what has been called the multiplication of a line as such by a line (it has been named ductus line in lineam, like the ductus plani in planum; there is also the ductus puncti in lineam) is an alteration not merely of magnitude, but of magnitude as a qualitative determination of spatiality, of dimensionality; the transition of the line into plane is to be understood as the self externalization of the line, just as the self externalization of the point is a line and the self externalization of the plane a whole space.