  We give a self contained proof using Seiberg Witten invariants that for
K\"ahler surfaces with non negative Kodaira dimension (including those with
$p_g = 0$) the canonical class of the minimal model and the $(-1)$-curves, are
oriented diffeomorphism invariants up to sign. This implies that the Kodaira
dimension is determined by the underlying differentiable manifold (Van de Ven
Conjecture). We use a set up that replaces generic metrics by the construction
of a localised Euler class of an infinite dimensional bundle with a Fredholm
section. This allows us to compute the Seiberg Witten invariants of all
elliptic surfaces with excess intersection theory. We then reprove that the
multiplicities of the elliptic fibration are determined by the underlying
oriented manifold, and that the plurigenera of a surface are oriented
diffeomorphism invariants.
