A like judgment must be passed upon what is called liberty of teaching. There can be no doubt that truth alone should imbue the minds of men, for in it are found the well-being, the end, and the perfection of every intelligent nature; and therefore nothing but truth should be taught both to the ignorant and to the educated, so as to bring knowledge to those who have it not, and to preserve it in those who possess it. For this reason it is plainly the duty of all who teach to banish error from the mind, and by sure safeguards to close the entry to all false convictions. From this it follows, as is evident, that the liberty of which We have been speaking is greatly opposed to reason, and tends absolutely to pervert men's minds, in as much as it claims for itself the right of teaching whatever it pleases -- a liberty which the State cannot grant without failing in its duty. And the more so because the authority of teachers has great weight with their hearers, who can rarely decide for themselves as to the truth or falsehood of the instruction given to them. Wherefore, this liberty, also, in order that it may deserve the name, must be kept within certain limits, lest the office of teaching be turned with impunity into an instrument of corruption. Now, truth, which should be the only subject matter of those who teach, is of two kinds: natural and supernatural. Of natural truths, such as the principles of nature and whatever is derived from them immediately by our reason, there is a kind of common patrimony in the human race. On this, as on a firm basis, morality, justice, religion, and the very bonds of human society rest: and to allow people to go unharmed who violate or destroy it would be most impious, most foolish, and most inhuman. (Papal Writings, Libertas, 1888).