Does the Catholic Church teach that the Catholic faith is demonstrably true? Question: Does the Catholic Church teach that the Catholic faith is demonstrably (with certainty) true? Please provide references.

Thanks for any help.
No, not all the truths of the faith are demonstrable.
First Vatican Council, Dei Filius IV canon 1 on faith &amp; reason:


If any one shall say that in divine revelation there are no mysteries, truly and properly so called, but that all the doctrines of faith can be understood and demonstrated from natural principles, by properly cultivated reason: let him be anathema.[Cdl. Manning's transl. of:] Si quis dixerit, in revelatione divina nulla vera et proprie dicta mysteria contineri, sed universa fidei dogmata posse per rationem rite excultam e naturalibus principiis intelligi et demonstrari: anathema sit. 


Some truths of the faith cannot be demonstrated, such as the Trinity, although they can be shown not to be contrary to human reason. St. Thomas Aquinas, the greatest Doctor of the Church, said in his Summa Theologica I q. 32 a. 1 c.:

It is impossible to attain to the knowledge of the divine persons of the Trinity by natural reason.
impossibile est per rationem naturalem ad cognitionem Trinitatis divinarum personarum pervenire.

Thus, faith is necessary to understand &quot;what belongs to the distinction of the persons,&quot; St. Thomas continues, and &quot;by natural reason we can [only] know what belongs to the unity of the essence [of God].&quot;
See the first chapters of St. Thomas's Summa contra Gentiles book 1, esp. these:

On the way in which divine truth is to be made known
That the truth about God to which the natural reason reaches is fittingly proposed to men for belief
That the truths the human reason is not able to investigate are fittingly proposed to men for belief
That to give assent to the truths of faith is not foolishness even though they are above reason
That the truth of reason is not opposed to the truth of the Christian faith
How the human reason is related to the truth of faith

Even Aristotle realized that not all truths are demonstrable.