25 “All human beings desire to know”, and truth is the proper object of this desire. Everyday life shows how concerned each of us is to discover for ourselves, beyond mere opinions, how things really are. Within visible creation, man is the only creature who not only is capable of knowing but who knows that he knows, and is therefore interested in the real truth of what he perceives. People cannot be genuinely indifferent to the question of whether what they know is true or not. If they discover that it is false, they reject it; but if they can establish its truth, they feel themselves rewarded. It is this that Saint Augustine teaches when he writes: “I have met many who wanted to deceive, but none who wanted to be deceived”. It is rightly claimed that persons have reached adulthood when they can distinguish independently between truth and falsehood, making up their own minds about the objective reality of things. This is what has driven so many enquiries, especially in the scientific field, which in recent centuries have produced important results, leading to genuine progress for all humanity. No less important than research in the theoretical field is research in the practical field—by which I mean the search for truth which looks to the good which is to be performed. In acting ethically, according to a free and rightly tuned will, the human person sets foot upon the path to happiness and moves towards perfection. Here too it is a question of truth. It is this conviction which I stressed in my Encyclical Letter Veritatis Splendor: “There is no morality without freedom... Although each individual has a right to be respected in his own journey in search of the truth, there exists a prior moral obligation, and a grave one at that, to seek the truth and to adhere to it once it is known”. It is essential, therefore, that the values chosen and pursued in one's life be true, because only true values can lead people to realize themselves fully, allowing them to be true to their nature. The truth of these values is to be found not by turning in on oneself but by opening oneself to apprehend that truth even at levels which transcend the person. This is an essential condition for us to become ourselves and to grow as mature, adult persons.
Source: Fides et Ratio (Vatican.va)