We may pause a moment to inquire about the chants which bear his name, but we shall have slight enough information. Four tunes are traditional: the Dorian, Phrygian, Lydian, and Mixed Lydian. What these were and how they were sung, we do not accurately know. We do know, however, that Ambrose employed but four notes (the _tetrachord_) where we have subdivided the various tones into the octave. The Germans do not profess to tell us anything more definite than this.
The actual hymns are to be reckoned up in several ways. First comes the mass of _Ambrosiani_, including hymns of Gregory the Great and of other and much later authors. Many have been foisted into this category because they were found in old breviaries and manuscripts. Then from these we may separate the _presumed originals_—of which a large proportion are now known to belong to other writers. These misapprehensions are due to such compilers as Fabricius, Cassander, Clichtove, and Thomasius, who were not invariably correct and who perpetuated their designations through later works. Still a third class are the _possible originals_, selected by the judicious but not always accurate zeal of the Benedictines of St. Maur when they edited the collected works of the great bishop. And last of all can be placed the _probable originals_—those hymns which are authenticated by Augustine and by St. Caelestin (A.D. 430), together with those in structure closely resembling them.
For our own purposes a fifth class can even yet be formed from the last named group—the _undoubted originals_, which will comprise only those attested by contemporary authority.
The list would stand then in the order of authenticity, about as follows:
Attested by St Augustine. _Deus Creator omnium_, _Aeterne rerum conditor_, _Jam surgit hora tertia, Qua_ Referred to directly by St. Caelestin. _Veni Redemptor gentium._
These are the _undoubted_ hymns and the only hymns to be safely assigned to Ambrose.
_Aeterna Christi numera, et martyrum_, _Illuminans altissimus_, _Orabo mente dominum_, (from _Bis ternas horas_,) _Splendor paternae gloriae_.
_Apostolorum passio_, _Conditor alme siderum_, _Consors paterni luminis_, _Hic est dies verus Dei_, _Jam lucis orto sidere_, _Nunc sancte nobis Spiritus_, _O lux beata Trinitas_, _Obduxere polum nubila coeli_, _O rex aeterne domine_, _Rector potens, verax Deus_, _Rerum Deus tenax vigor_, _Somno refectis artubus_, _Squalent arva soli pulvere multo_, _Summae Deus clementiae_, _Tristes erant apostoli_.