  We discuss the dependence of superpotential terms in 4D F-theory on moduli
parameters. Two cases are studied: the dependence on world-filling 3-brane
positions and the dependence on 2-form VEVs. In the first case there is a zero
when the 3-brane hits the divisor responsible for the superpotential. In the
second case, which has been extensively discussed by Witten in 3D M-theory,
there is a zero for special values of 2-form VEVs when the M-theory divisor
contains non-trivial 3-cycles. We give an alternative derivation of this fact
for the special case of F-theory.
