While reading about how magnetic flux works, I've come across two concepts that seem to contradict each other: Concept A: http://www.emfs.info/what/adding/ adding magnetic fields is simply vector addition. In other words, magnetic fields are always acting independently, and the sum of flux at any given location in space the just the sum total of independently behaving magnetic fields at that point in space. Concept B: putting magnets or permeable materials close together alters the "return path" of their magnetic flux lines. For example, a "closed core" transformer versus a "shell core", where the idea behind the shell is to bring the magnetic return path of the coil closer to the coil. This would suggest that the magnet flux of any given atom is not a fixed shape, but that it's shape can altered by other magnetic fields, which contradicts the idea that a combination of magnetic fields is simple vector addition. Are magnetic lines of flux really "shaped" by the other magnetic things around them, or do they always maintain a particular shape no matter what, and the concept of guiding "returns paths" merely an abstraction?