Of course, anybody is entitled to comment on the tentative sequence of ideas, tersely summarised, that follows; but I will most appreciate contributions from those with some expertise in fields where I only stumble. Others are warned that a lot of what follows is plagiarised without explicit acknowledgement from authoritative or weighty sources; if you tell me that I am being ridiculous, it may not prove to only be Fr H that you are deriding, but also somebody whom you respect.
LAW. >We are not in conscience obliged to obey a law the authority of which is uncertain. Lex dubia non obligat; non potest lex incerta certam obligationem inducere; nemo ad aliquam legem servandam tenetur, nisi illa ut certa ei manifestetur.
>How are we to know whether in a particular matter a law is certain? Of the systems proposed in the old manuals, Probabilism seems to many of us, despite the views of Professor Pruemmer, the most persuasive. If in doubt between two or more moral possibilities each of which can be characterised as Probable, we may follow even that possibility which is the less or least probable, provided that it is genuinely still probable.
LITURGICAL LAW. >Rubrics are either substantial, because they prescribe the form or matter of a Sacrament; or accidental when they do not prescribe form or matter.
>They also fall into these categories: Preceptive; directive; facultative.The last category consists of rubrics which explicitly permit a choice; I shall not trouble with them further. Substantial rubrics are preceptive and bind in conscience. The question to interest us is whether accidental rubrics are all, necessarily, preceptive; or whether some among them are only directive. If some are merely directive, this means that they do not in themselves bind in conscience, but simply provide the approved way of carrying out a liturgical action.
>Most moral theologians, and many of the old rubrical experts, hold, with varying degrees of emphasis, that some rubrics are only directive. They feel that the Church does not intend that small details should oblige sub gravi. They tend not to be very generous in suggesting examples. It is, perhaps, easy to guess why.
>Even among those who incline to believe that all rubrics are preceptive, there is sometimes an inclination to feel that some wiggle-room is necessary. A distinguished example of this is Benedict XIV writing as a private theologian; having reported that a communis sententia is that rubrics are preceptive, he adds that one can be immune from mortal sin when breaking a rubric "propter parvitatem materiae". Herein lies a problem. What is 'parvitas materiae'?
CONCLUSIONS. >If we put together the two parts of this note, we find that the question whether each and every rubric binds in conscience or not, is an open question. Since the question is open, one is in conscience free to choose and follow even a less probable judgement, provided always that it still does have a degree of probability.
>I cannot think of any explicit post-Conciliar legislation which intimates that the rubrical requirements of the post-Conciliar rites are less - or more - stringent than the assumptions which accompanied the Old Rites (can you?). But I venture to suggest that the usage of the Church and the extent and type of disciplinary intrusions by authority at every level may indicate a communis sententia that we are less rigorist now than we were in my youth.
CUSTOM. The old writers devote some energy to the question of custom acquiring the force of Law even when the custom is contrary to the letter of the law (contra legem). They are able to show that the SRC operated itself upon this principle. I omit a detailed discussion of this point because I suspect that the necessary time may not yet have elapsed since the promulgation of the post-Conciliar rites for this to be relevant, i.e. for immemorial and unreprobated custom to have become established.
EXAMPLE. Saying the Canon silently is OK.