Is cosmology just a plausibility argument?
  I review the basis and limitations of plausible inference in cosmology, in
particular the limitation that it can only provide fundamentally true
inferences when the hypotheses under consideration form a set that is
exhaustive. They never do; this recommends abandoning realism. Despite this, we
can adopt a scientifically correct pragmatism and understand aspects of the
cosmological model with enormous confidence. I illustrate these points with
discussion of one certainty--expansion--and two current controversies--the
existence of large extra dimensions and the possibility that the matter
distribution forms a fractal on large scales. I argue that the existence of
large extra dimensions is certainly plausible, but a fractal universe is
untenable.
