Desargues wrote other books besides the one on conic sections, one of them being a treatise on how to teach children to sing well. But it is the little book on conic sections that marks him as the most original contributor to synthetic geometry in the seventeenth century. Starting with Kepler’s doctrine of continuity, the work develops many of the fundamental theorems on involution, harmonic ranges, homology, poles and polars, and perspective-topics familiar to those who have taken one of our present-day courses in
projective geometry.