Those authors find that, in texts of the sort we are studying, attitude predicates are used predominantly to mark the source of information that is effectively asserted despite being embedded (Rooryck, 2001;Simons, 2007).
though X said p does not semantically entail p, it is often interpreted as a commitment to p, which correspondingly elevates mentions in p to main-clause status (Harris and Potts, 2009).