 We must therefore distinguish distinct ways of associating the principles with various domains. The first way is to specify the domain to which each principle applies. Leibniz appears to believe that, according to this approach, there is a single universal domain and it is associated equally with each principle. There are no contradictory contingent facts or truths and so the Principle of Noncontradiction applies to all contingent truths as well as all necessary truths. Likewise, it is usually assumed that, for Leibniz, every necessary truth has a sufficient reason (see Broad 1975: 12 and 34 and Rodriguez-Pererya forthcoming). For example, mathematical truths, might have sufficient reasons in the form of proofs that rest on statements of identity. Thus the PSR applies to all necessary truths as well as all contingent truths.