Full Idea
If one endorses a theory, so one might argue, one should also take it to be sound.
Gist of Idea
Normally we only endorse a theory if we believe it to be sound
Source
Volker Halbach (Axiomatic Theories of Truth [2011], 22.1)
Book Reference
Halbach,Volker: 'Axiomatic Theories of Truth' [CUP 2011], p.322