  We consider deformations of the scalar curvature of a partially integrable
pseudohermitian manifold, in analogy with the work of Fischer and Marsden on
Riemannian manifolds. In particular, we introduce and discuss $R$-singular
spaces, give sufficient conditions for the stability of the scalar curvature,
and give a partial infinitesimal rigidity result for the scalar curvature of a
compact, torsion-free, scalar-flat, integrable pseudohermitian manifold.
