When is "diēs" masculine, when is it feminine, and why can this word take different genders?

Question

Wiktionary goes into it a bit:

Diēs is an exceptional case of a fifth declension noun since it is both used in the masculine form and in the feminine form, instead of just feminine like the rest of the fifth declension nouns. The masculine use is more common, and almost invariably used for the plural. The feminine use is found in the singular when the day is being personified as a goddess, when it refers to a specific day (e.g., the date of a letter, or an appointed day for business), when it refers to the passing of time, and occasionally in other contexts.

But why, etymologically, is this the case? Why these different categories? Do we have evidence that these uses change over time?

Answer 1

I believe there's no straightforward answer as to „why different usage contexts correlate to different grammatical gender“, but the etymological origin gives some insights to the gender.

Diēs comes from Proto-Indo-European *d(i)jéus „daytime sky, Sky-god“ and is cognate to Iūp-piter (≈ Diespiter, „dies pater“), so originally it should have been masculine, as it is the name of a father god (= Vedic dyauḥ [pitā] or Greek Ζεῦς [πατήρ]):

The Latin forms Diespiter, Dispiter, U. di, dei together with the word diēs ‘day’ point to the generalization of a stem *dijē-, whereas Iūpiter, Iovis reflect PIt. *djow-. These can be derived from a single PIE paradigm for ‘(god of the) sky, day-light’, which phonetically split in two in PIt. and yielded two new stems with semantic specialization. Syllabic *dij- in the nom.acc.sg. can stem from the oblique cases (gen.sg. *diwos, etc.), in which syllabic *di- occurred. The acc.sg. *dijēm led to the creation of a new nom.sg. *dijēs and a separate paradigm meaning ‘day’ <..>

(Michiel de Vaan, Etymological Dictionary of Latin and the Other Italic Languages, Brill, 2008)

As for feminine diēs, I guess that it might be a paradigm-leveling – fifth declension is regularly feminine, diēs is the only masculine exception, so by analogy it would be inclined to become feminine too. However, I am not sure if this is exactly the factor, I couldn't find a source – please suggest one or disprove this.

Answer 2

I can only partially answer your question. In medieval documents dies is sometimes feminine where based on classical usage we would expect it to be masculine. Examples:

1. Liber Pontificalis¹ (~10th century) 371, in reference to Charlemagne's arrival in Rome (but note that this text contains frequent grammatical irregularities):

Et alia die, secundum olitanam consuetudinem, natale beati Andreae apostoli celebrantes, Roma introeunte cum mole gaudio et laetitia in patriarchio Lateranense introivit.

2. Ekkhart (12th century) uses dies in the feminine in all of its three occurrences in the excerpts in Sidwell.² (But it could be that these are feminine because they refer to the dies dicta of the meeting between Henry IV and the Pope.)

   • "quam ingenti periculo, quam varia disceptatione tota dies illa consumpta sit"
   • "quod et impigre fecit et usque ad inclinatam iam diem"
   • "Sic denique ea die gloria in excelsis Deo et in terra pax hominibus bonae voluntatis, ut ita dicam, est recuperata"

3. Roger Bacon (13th century), in the DMLBS³ (but from which Bacon text I don't know): "dicitur ... dies alia longior esse".

4. See elsewhere in the DMLBS entry, where dies is used in either gender, e.g. dies festus/festivus vs. dies festiva.

References

1. Le Liber Pontificalis: Texte, Introduction et Commentaire, vol. II. 1892. Ed. L’Abbé L. Duchesne.

2. Sidwell, Keith. 1995. Reading Medieval Latin. At 12.3.ii-iii, pp. 202-203.

3. Dictionary of Medieval Latin from British Sources ad loc. via Logeion.

Answer 3

The OLD writes that dies is "fem. frequently or usually in senses 1b, 5, 7, 10, occasionally elsewhere," with the following definitions listed:

• 1b: [the period from sunrise to sunset] as a deity
• 5: A specific day, the date of a letter
• 7: A day appointed for business
• 10: The lapse or passing of time

You might want to scope out the OLD for more about those definitions — lots of good, broad examples.

For what it's worth, I have always used the first part of Ovid Met 10.270 (from the Pygmalion episode) to help me remember that specific days/festival days are generally feminine:

Festa dies Veneris...

Answer 4

Diēs was originally an irregular member of the fourth declension: in Old Latin the nom. was diūs. But the irregular acc. diēm tended to generate a new nominative by analogy, and the noun was pulled into the emerging fifth declension while keeping its gender. These 12 or so nouns don't represent any identifiable group of PIE nouns, but slowly became more similar to each other over time; rēs, for example, was originally thoroughly irregular. Many of them are defective in the plural, either altogether or in particular cases only.