A standing wave in fresh water provides the first mental model.
Watch a trout stream moving over and around submerged rock. The water passes through. A visible wave may remain in place, or a disturbance may travel while individual parcels of water do not accompany it across the full distance. The material is continuously exchanged, yet the relation persists. The form is handed from one parcel to the next.
This separates two events that language easily confuses. Matter may move through space. Form may also be transformed and re-formed through a medium. The second does not require the first to travel with it as a permanent material object.
The wave is real, but it is not a parcel. What persists is the organized relation among successive parcels.
Music makes the same distinction available to ordinary experience. A melody can be played in another key, at another octave, by another instrument, transmitted through air, stored in a groove, represented as notation, or held in memory. None of those substrates is the melody. Yet the melody is not imaginary. Its identity rests in a relation stable enough to survive the hand-off.
This is not an argument that all forms are independent of matter. No melody is heard without an execution, and no water wave occurs without a medium. It is an argument about what remains invariant when the carrier changes. The carrier supplies the conditions of appearance. The pattern supplies the relation that can appear again.
The distinction between motion and transformation becomes increasingly important as the inquiry moves toward life. Before asking how a form reproduces, we need to see that persistence already exists in nonliving systems. The wave can persist while its material changes. A flame can maintain a recognizable boundary while fuel enters and products leave. A vortex can remain while the fluid composing it is replaced. Life does not invent the possibility that a form can outlast its present matter. Life changes what the form can do with that possibility.