Why does the dependence of Coulomb force on the medium not conflict with the superposition principle? 
Why does the dependence of Coulomb force on the medium not conflict with the superposition principle?

As I have been told (and checked myself on the web including this website), the Coulomb force changes by a factor when the medium is changed, due to the polarisation of the medium.
But the polarisation is basically just charged particles, and the superposition principle states that the force on one charge by another doesn't depend upon any other charge. So, why does the Coulomb force on one charge by another change?
My teacher has a different opinion. He says that the Coulomb force doesn't actually change, but the net force changes, and the difference actually comes from the force on the charge by the charges in the medium.
PS. I am just a beginner and only know the very basics, so it would be better if the answer is in elementary terms.
 A: Your teacher is correct.
The force on one charged particle due to another does not change. But the medium (due to polarization) changes the net force on the particles.
When the medium becomes polarized due to the presence of the charges, the electric field on each particle will be different compared to the case of the
charges in a vacuum, meaning the net force on the particles will also be different than if in a vacuum.
Technically, the electrostatic force between the two charged particles will not depend on the medium,
but the net force each charge experiences will depend on the medium.
The difference between the net force and the vacuum coulomb force is indeed due to the sum of the individual coulomb forces
of the charges of the molecules in the polarized medium and the original charged particles.
So there is no contradiction between this and the superposition principle.
A: In simple terms: think about two charges A and B in vacuum, the Coulomb force acts on each charge. If the medium is changed, taking for example dielectric, the electric field of the charges change the orientation of the dipoles of the medium. It means that the medium is polarized. Polarization is the average dipole per volume. Then the medium itself create an electric field due to this polarization. So the total electric field acting on B, for example, is the sum (superposition principle) of the electric field generated by the charge A and the electric field of the medium, that is opposite in direction respect to the original field in vacuum, reducing the total field and hence the force by a factor called permittivity.
*Taking linear, homogeneous and isotropic response of the medium to external electric field.
