What does it mean to not have an inner life? In the
extreme case, to me, this means having no thoughts or
feelings of one's own. This is an impossibility, but there
are people who seem to have few thoughts or feelings
of their own, only able to "mirror" those around them.
What are the implications of this? As you consider what
the implications are, one of them is likely to be your
thesis. One thought that comes to my mind is that no
one has an real inner life because all of our minds are
formed by way of what is outside of us, since the only
way any information or idea can enter our brains is
through sensory experiences in the external world, our
interactions with things and people. This would be an
argument that the statement applies to all humans.
Aside from making this argument, assuming for the
purposes of the assignment that the statement is true, I
think first that such a person cannot bear to be alone,
since he or she has no inner resources upon which to
draw in solitude, with a countervailing example of the
person who prefers to be alone because he or she has a
rich inner life, and second that such a person is quite
easily led. This provides three possible theses for an
essay. I am sure you will be able to think of some other
possibilities, too.