  We consider compactifications of the N=1, d=6, E_8 theory on tori to five,
four, and three dimensions and learn about some properties of this theory. As a
by-product we derive the SL(2,\IZ) duality of the N=2, d=4, SU(2) theory with
N_f=4. Using this theory on a D-brane probe we shed new light on the
singularities of F-theory compactifications to eight dimensions. As another
application we consider compactifications of F-theory, M-theory and the IIA
string on (singular) Calabi-Yau spaces where our theory appears in spacetime.
Our viewpoint leads to a new perspective on the nature of the singularities in
the moduli space and their spacetime interpretations. In particular, we have a
universal understanding of how the singularities in the classical moduli space
of Calabi--Yau spaces are modified by worldsheet instantons to singularities in
the moduli space of the corresponding conformal field theories.
