# Electric Fields 'passing' through conductor material

I've been reading Chapter 3.2 and 3.3 of Purcell's Electricity and Magnetism, 3rd ed, and found that I don't really understand a few ideas that Purcell makes about electric fields and conducting material.

An example is given with a point charge q placed arbitrarily inside a neutral conducting spherical shell. The example explains why the electric field outside the shell is the same as a spherically symmetric field due to charge q located at the center of the shell.

In finding how +q charge is induced on the outside of the conductor, the example tells us to imagine we remove the outer +q charge so we only have the point charge q and inner surface charge -q -- they claim the combination of these charges produces zero field in the material of the conductor and outside the conductor, because 'field lines must have at least one end on a charge and can't form closed loops. In the present setup, external field lines have no possibility of touching any of the charges on the inside, because the lines can't pass through the material of the conductor to reach them, since the field is zero there. Therefore there can be no field lines outside the conductor.'

What do they mean by this? It is my understanding that the -q inner surface charge distributes itself in such a way that the superposition of its electric field and the electric field of the point charge q equals 0 anywhere in the conductor material -- and 0 anywhere outside the conductor. However, that would mean field lines have to pass the conductor material.

And in section 3.3, Purcell wants us to consider a closed metal box with some external charges outside -- he notes that there is a nonuniform distribution of charge over the surface of the box. He then claims that the field everywhere in space, including the interior of the box, is the sum of the field of the charge distribution over the surface and the fields of the external sources.

However, this again implies that external field lines pass through the conductor material, in order to sum to 0. Is it the case that I'm misinterpreting the first example? What then does it mean in that scenario that 'external field lines have no possibility of touching any of the charges on the inside ... there can be no field lines outside the conductor'?