Use as it is in this location of the code it becomes a subjective word and in my mind it means in the same raceway, cable or trench.
There is a condition for running the grounding conductor separate from the other conductors as defined in 250.130(C) for receptacles and extentions and I would accept a single conductor for that type of installation. For example where it is a NM cable job. But after seeing what you guy/gals have posted I'm convinced that the proper installation would be to have the IG installed in the same wiring method as discribed above.
