29 It is unthinkable that a search so deeply rooted in human nature would be completely vain and useless. The capacity to search for truth and to pose questions itself implies the rudiments of a response. Human beings would not even begin to search for something of which they knew nothing or for something which they thought was wholly beyond them. Only the sense that they can arrive at an answer leads them to take the first step. This is what normally happens in scientific research. When scientists, following their intuition, set out in search of the logical and verifiable explanation of a phenomenon, they are confident from the first that they will find an answer, and they do not give up in the face of setbacks. They do not judge their original intuition useless simply because they have not reached their goal; rightly enough they will say that they have not yet found a satisfactory answer. The same must be equally true of the search for truth when it comes to the ultimate questions. The thirst for truth is so rooted in the human heart that to be obliged to ignore it would cast our existence into jeopardy. Everyday life shows well enough how each one of us is preoccupied by the pressure of a few fundamental questions and how in the soul of each of us there is at least an outline of the answers. One reason why the truth of these answers convinces is that they are no different in substance from the answers to which many others have come. To be sure, not every truth to which we come has the same value. But the sum of the results achieved confirms that in principle the human being can arrive at the truth.
Source: Fides et Ratio (Vatican.va)