al certainty that he has satisfied the precept, and it is not
necessary to repeat it; if the necessity for repetition be admitted in
such a case, a fruitful source of scruples is opened up.

On the other hand, if the doubt be negative--that is to say, if a person
has no reasonable motive for believing that he has recited the full
office or the full hour, he is bound to recite the part omitted,
because in such a doubt, the precept of recitation is, as the
theologians say, "in possession." (St. Alphonsus, n. 150).

It is not allowed to change anything nor to add anything to the daily
office without permission. The Sacred Congregation of Rites (10 June,
1690, n. 3222) replied to a query, that in saints' offices nothing is to
be added and nothing is to be changed, and this reply applies to all
sorts of offices, old and new.

THE ORDER TO BE OBSERVED IN RECITING THE DIVINE OFFICE.

In reciting the Divine Office two points of order are to be noted: (1)
the order or arrangement of offices, (2) the order or arrangement of
Hours. The order of offices indicates which office is to be said on each
day as laid down in the calendar. The order of the Hours points out
which of the seven hours should be recited, firstly, secondly, etc.,
Matins, Lauds, Prime, Terce, etc. It is of obligation to observe both
orders. But is it a sin to change wilfully the order of the office? It
is not, if there be a reasonable cause for the change. For instance, if
a priest cannot say the office proper to his diocese on a certain day,
but says some other approved office, the change is not a sin. But if a
priest, _ex industria_, substitute one office for another, it is _per
se_ a venial sin; but if an office be said which is very much shorter
than the calendar office, or if this changing or substituting be so
frequent as to disturb gravely the good order of the year's offices, the
sin may be (and, according to some authors, is) a mortal sin.

It is asked whether a person fulfils his debt to the Church if he has
recited by mistake an office other than the one assigned in the calendar
of the day. Theologians teach that such a recitation fulfils the debt.
The Church does not wish to impose a second recitation, and her axiom
"_officium pro officio valet_" holds, provided always that the order of
the psalms as laid down in the new psaltery is followed. This order is
necessary always for validity. However, if the substituted office be
very much shorter