150

G128

that there are any concepts that are, in their own nature, simple. At the time I wrote those articles I was possessed with the notion that, for example, a straight line is not of the very nature of straightness, any simpler than almost any curve of a family of curves any pair of which should, in the space of ordinary projective geometry, cut each other in one point at the utmost, and such that all those that cut any two intersecting lines of the family should lie on one surface, such that any two such surfaces should cut one another in a line of the family, and any three (not having a line in common) in a single point; and further, so that there should be one such surface through any [of] those points. It is very easy to prove