This is the closest I've been able to find in St. Thomas, where he discusses whether truth is immutable ([_Summa Theologica_ I q. 16 a. 8][1] ad 3):

>A proposition not only has truth, as other things are said to have it, in so far, that is, as they correspond to that which is the design of the divine intellect concerning them; but it said to have truth in a special way, in so far as it indicates the truth of the intellect, which consists in the conformity of the intellect with a thing. When this disappears, the truth of an opinion changes, and consequently the truth of the proposition. So therefore this proposition, "Socrates sits," is true, as long as he is sitting, both with the truth of the thing, in so far as the expression is significative, and with the truth of signification, in so far as it signifies a true opinion. When Socrates rises, the first truth remains, but the second is changed.


  [1]: http://dhspriory.org/thomas/summa/FP/FP016.html#FPQ16A8THEP1