"Human law is law only by virtue of its accordance with right reason; and thus it is manifest that it flows from the eternal law. And in so far as it deviates from right reason it is called an unjust law; in such case it is no law at all, but rather a species of violence." 

-- Thomas Aquinas, Summa theologiae, Ia-Ilae, q. xciii, art. 3, ad 2m.
 
 
_"Human law is law only by virtue of its accordance with right reason; and thus it is manifest that it flows from the eternal law. And in so far as it deviates from right reason it is called an unjust law; in such case it is no law at all, but rather a species of violence." 

-- Thomas Aquinas