I've had a question from a reader that I suspect puzzles many people, so I thought I'd answer it here.
The question is: Why does the numbering of psalms in the Monastic Diurnal often diverge from that in many contemporary Bibles?
On the psalm numbering, basically the problem is that there isn't really any set numbering or versification in the book of psalms, so later manuscripts have added it in for convenience sake, and there are (at least) two distinct traditions on how to divide up the psalms.
In some cases the appropriate divisions between psalms is reasonably obvious, for example because there are 'titles' to the psalms (not used for liturgical purposes).
But the split of a number of psalms differs between the 'Hebrew Bible' (Maseoretic Text manuscript tradition) which forms the basis of many modern translations (and protestant Bibles), and the Greek Septuagint (the translation made a few centuries before Christ). In some cases the Septuagint provides different titles as well, possibly reflecting different manuscript traditions.
The 'Vulgate' of the traditional psalter basically follows the Septuagint, but most modern Bibles follow the Hebrew Bible, hence the differences in numbering.
There has been debate on which tradition is better going back to the time of St Jerome when he made his series of translations into Latin (St Jerome preferred the Hebrew base texts, but made several versions including from the Greek; St Augustine preferred the Greek). For centuries the Church stuck with the Greek as its base text for the psalms, partly because of its Greek liturgical tradition in the Church, and partly because of the heavy use of the Septuagint by the NT writers (and the book of psalms is the most quoted of Old Testament books in the New).
The neo-Vulgate now used as the official base text for translations into the vernacular however, has adopted the Hebrew psalm numbering system, presumably for ecumenical reasons.
Aligning psalm numbers
The way it works is as follows:
Psalms numbers 1-8 and 148-150 are the same in both systems.
Vulgate 9, 10 = Hebrew 9
Vulgate 113 = Hebrew 114, 115
Vulgate 146, 147 = Hebrew 147
So for Vulgate psalms 10 – 112, add one number to get Hebrew number (ie 11-113)
So for Vulgate psalms 116-145, add one to get Hebrew number.
Note that verse references too vary between versions - the Vulgate of the psalter has been divided up into readily singable lines, but this sometimes cuts across the natural flow of the verses, used in Bible versions intended for other purposes.