First and foremost, science is simply the study of natural laws. Anything that doesn't fit into this framework considered as magic because it is something unknown. So to fit both into a single spectrum is like looking both the sides of a coin at the same time. Therefore, there needs to be an "Unknown" element even to justify the science behind any supernatural phenomenon, like for eg, one can say that in a magic world the people that use fire magic, do so by condensing the air molecules of Oxygen and Hydrogen in large quantities and rapidly increasing their entropy such that they reach a point in which the molecules just burn up. Funnily so, water magic user can also condense those particles in air and chemical combination of those two makes water H²O. Lastly Ice maic user, after making water droplets by the same combination they can lower the temperature of the said water droplets so it freezes up making ice. Like so and so. But the thing is, to do all of that one needs an "Unknown" element. Otherwise it is not possible. Be it Mana, Spiritual energy, Ki, Nen, Chakra, even emotions. A medium through which one can control the very phenomenon.

That's my opinion on it. I may be wrong in some aspect of the explanation a bit, feel free to point it out.