Note 137 — Introductory material

The next step in the argument, which assumes two or more dimensions, is concerned with the general analogues of straight lines and planes, i.e. with figures—which may be regarded either as relations between positions or as series of positions—uniquely determined by two or by three positions. If this step can be successfully taken, our deduction of the above projective axioms will be complete, and descriptive Geometry will be established as the abstract à priori doctrine of forms of externality.