The approach to 'validity' which is employed by some modern writers seems to me excessively, grossly, legalistic and fails to take account of the older, broader, more humane approach of earlier Catholic theologians. In order to summarise this tradition, I will quote from the well-judged words of Cardinal Pietro Gasparri, the great and massively erudite Father of modern Canon Law*. Perhaps I should explain that he was writing at a time when the universal opinion was that the Form of Episcopal Consecration was the formula Accipe Spiritum Sanctum, said by the consecrator as he imposed hands; but a time also when scholars had become aware that, in the ancient Roman Sacramentaries, the Form had been the ancient prayer which came down to us disguised as a Prefacestructured as a Preface.
"Among all these rites which the Roman Pontifical prescribes in Episcopal Consecration, the common opinion is that the Matter is the imposition of the hands of the consecrating bishop (rather, of the consecrating bishops) and the Form is the related words Receive the Holy Spirit.
"We think ... that, in the hypothesis of the imposition of the bishop's hands with the Preface alone, without those words Receive the Holy Spirit, the Consecration is valid, just as it was valid in the ancient liturgy; for how could you prove that the Church had taken its consecratory power away from this Prayer?
"Equally, in the hypothesis of the imposition of the bishop's hands with those words alone Receive the Holy Spirit, without the Preface, we admit, with the common opinion, that the ordination is valid, since, although those words alone, considered in themselves, are indeterminate and do not sufficiently express the conferring of the episcopal order, nevertheless they are made sufficiently determinate not only by the Preface but by the caeremonia itself without the Preface."
And, of course, if 'determination' can be given to indeterminate wording such as Receive the Holy Spirit, then 'determination' can also thus be given to a phrase such as pneuma hegemonicon in the post-Conciliar Pontificale. Especially if it occurs in formulae which have for centuries been accepted in the praxis of the Roman See as adequate to confer the episcopate.
So Gasparri's generously sensible approach* is, I think, more than sufficient to put paid to scaremongering nonsense about the validity of the ministerial orders of the post-conciliar Church.
But it is not enough for us simply to be able to dismiss an erroneous argument. There is a great deal more to be said.
It ought never to have been made so easy for such erroneous arguments to be made. It ought never to have been made possible for the ancient and venerable sacramental formulae of the Roman Church to be dumped like so much rubbish by a committee of opinionated and self-important academics. It ought never to have happened that the transient scholarly opinion of a single academic generation became the basis of a liturgical revolution. It ought never to have happened that one man, Bugnini, was able to manipulate and deceive a Roman Pontiff and thereby debauch the euchology of the Roman Church. Credence should never have been given to the disgraceful notion that a Roman Pontiff, even if working on the basis of a conciliar mandate, could do anything that appealed to him.
*This common sense approach is not, I think, a million miles from the attitude of Fr Eric Mascall; that a rite is a means of doing something, not a theological statement of the nature of what is being done [for example, the word baptizo says nothing about regeneration or the deletion of Original Sin]; that a valid ordination rite can be recognised by its declared purpose of conferring a specified one of the three orders of the historic ministry.
Readers will not be surprised that I also share the view that the Eucharistic Prayer of Addai and Mari is adequate to confect the Holy Eucharist. A mens vere Catholica looks, not at a priori speculations about what 'ought' to be required for Sacramental validity, but at the praxis of the Catholic Church.