As for their assertion that, of any two existing things, one must be spatially coincident with the other or separate from it in some direction, they have two approaches to establishing this.

The first approach is to claim that it is self-evident. This approach, however, has already been discussed at the beginning of the book.

The second approach is to offer an argument for it. This is the approach adopted by Ibn al-Haysam in his account of his own debate with Ibn Fūrak.

Al-Rāzī said: I shall present the gist of those statements in