  In physical spacetime the projective structure has an immediate  intuitive significance according to Weyl. The real world is a  non-empty spacetime filled with an inertial-gravitational field,  which Weyl calls the guiding field   \((F\)ührungsfeld)[43].  It is an indubitable fact, according to Weyl (1923a, 13), that a body which is let free in a certain spacetime direction (time-like  direction) carries out a uniquely determined natural motion from  which it can only be diverted through an external force. The process  of autoparallelism of direction appears, thus, as the tendency of  persistence of the spacetime direction of a free particle whose  motion is governed by, what Weyl calls, the guiding field  \((F\)ührungsfeld). This natural  motion occurs on the basis of an effective infinitesimal tendency of  persistence, that parallelly displaces the spacetime direction  \(R\) of a body at an arbitrary point \(p\) on its trajectory  to a neighbouring point \(p'\) that lies in the direction  \(R\) at \(p\). 