The First Vatican Council contains a very direct condemnation of one of the main points of Modernism. It makes the following infallible statements:
13. For the doctrine of the faith which God has revealed is put forward not as some philosophical discovery capable of being perfected by human intelligence, but as a divine deposit committed to the spouse of Christ to be faithfully protected and infallibly promulgated.
14. Hence, too, that meaning of the sacred dogmas is ever to be maintained which has once been declared by Holy mother Church, and there must never be any abandonment of this sense under the pretext or in the name of a more profound understanding.
May understanding, knowledge and wisdom increase as ages and centuries roll along, and greatly and vigorously flourish, in each and all, in the individual and the whole Church: but this only in its own proper kind, that is to say, in the same doctrine, the same sense, and the same understanding....
...If anyone says that it is possible that at some time, given the advancement of knowledge, a sense may be assigned to the dogmas propounded by the Church which is different from that which the Church has understood and understands: let him be anathema.
This quite completely condemns the chief claim of the Modernists, namely that the Church's dogmas can change over the progress of time, so as to adapt to the ever evolving needs of humanity. But this also condemns one of the chief points of the Neo-modernists, who quite senselessly claim that while dogma does not change, the sense or meaning of the dogma, the way it is understood, can indeed change to be adapted to the times. This is also clearly condemned by Vatican I.
Indeed, this condemnation shows that it is quite unreasonable to try and separate dogma from its sense or meaning, from the way it is understood. If a dogma's meaning changes, the dogma itself changes, for the meaning of the dogma is the essence of the dogma. So how can a dogma be understood differently without the dogma itself actually changing? Ultimately then, Neo-modernism is just another form of the same old Modernism itself. Pope Pius XII makes this point in Humani Generis when he says of the Neo-modernist doctrines that “such tentatives not only lead to what they call dogmatic relativism, but that they actually contain it.”