28 But the need for serious reflection on truths which are already well known is in close accordance with the genius and mentality of our contemporaries, who like to explore their minds in depth. They find mental repose in the secure grasp of truth, apprehended, as it were, in the light of conscience. Not that this method of enquiry is without serious risk. Famous philosophers have studied this activity of the human intellect and pronounced it to be its most perfect and highest function. They have actually gone so far as to maintain that it is the measure and source of reality, and this has led them to some abstruse, barren, absurd, and wholly fallacious conclusions. Nevertheless, this does not mean that the training of the mind to scrutinize the truth which lies in the depth of its own awareness is not in itself an excellent thing. It is reckoned today as being the highest expression of modern culture. And if this mental discipline is carefully coordinated with that habit of mind whereby a man discovers objective truth, the investigation of one's conscious knowledge may well lead to a greater knowledge of oneself, one's dignity as a human being, one's intellectual powers and practical ability.
Source: Ecclesiam Suam (Vatican.va)