**Two triangles
are perspective from a line if the extensions of their three pairs of corresponding
sides meet in collinear**
**points. The line
joining these points is called the perspective axis.**
**Two triangles
are perspective from a point if their three pairs of corresponding vertices
are joined by lines which meet in a point of concurrence. This point is
called the perspective centre.**
**Desargues'
theorem guarantees that if two triangles are perspective from a point,
they are perspective from a line (and if they are perspective from a line,
they are perspective from a point).**

If we consider the Desargues' configuration as a 3D image, the proof of the theorem becomes obvious.