There is no notion of linear or angular measurement in projective geometry. Therefore there is no way to determine whether two lines are parallel. You may try to get around this by saying that two lines are parallel if they never meet, but this obviously is impossible to verify. Therefore there is no concept of parallelism in projective geometry, and in the formal structure of synthetic (axiomatic) projective geometry, it is assumed that every pair of lines eventually intersect. In the Thoth cards, you will notice that most of the "long" lines (those which appear to extend beyond the boundary of the card) look as if they are going to meet somewhere, either in the image itself or at some point outside of the image. I.e., Harris seems to be reluctant to depict linear parallelism in the images. This is in accordance with the nature of projective geometry. There is a notable exception in the grid behind the Hanged Man. The horizontal lines appear to be "parallel" and to extend beyond the boundary of the image. However, in projective geometry this is an illusion, and all of these horizontal lines must meet at some point, if not apparently at some finite point, at least at a hypothetical "point at infinity." The terminology is borrowed from perspective geometry, in which, for example the sides of a road, or parallel power lines, appear to converge to a point in the distance, called a point at infinity.