I just cannot decide whether, in a word beginning with the æ sound (which I always write as a ligature because I find it enormously æsthetically pleasing), when the word is capitalised in the beginning of a sentence (or is a name), I should write it as Æ or Ae. If the entire word was in capitals, then Æ is a given choice (ÆGYPTVS), but if I want to say ”Egypt is white” (to take a nonsense example), what is the best: ”Ægyptus est albus” or Aegyptus est albus”.
Both are good, neither is better, but AEgyptus is wrong.
Ambo bona sunt, neuter melius est. In AEgypti autem verbo E littera ut majuscula perperàm scribitur.
Or neither since “Aegyptus” (the country) is feminine 
But about the actual topic, I’ve seen both but Ae seems a lot more common according to google books. Æ feels more archaic (or French) to me.
Doh! Me ineptum!
That’s a pity when it comes to the machine readability of diphthongs in texts, apart from any desire to practice skills in recognizing and imitating older handwriting styles and font typefaces.
Quod paenitet, quoàd diphthongos facilè legere computatris difficile est, separatim utile ad studium exercitationemque artium palaeographicarum et scripturarum typographicarum est ligaturas advertere.
Eodem tempore // At the same time:
But I do use æ 
The problem is that there are no OpenType fonts that replaces ae with æ and oe with œ, they have to be typed manually. Quite a pity - but non the less, one can use them in places like this and that is pretty fin i.m.o. :3.
I don’t think they’re counting ligatures such as æ and œ, because they are rather distinct from ‘ae’ and ‘oe’. It refers to typesetting ligatures such as ‘fi’, which has the dot if the ‘i’ merged with the top of the ‘f’. (It’s generally used in serif fonts, which is why you might not see the ligature in this post.) Here are examples of this and others from Wikipedia. This is quite a different thing; the use of a ligature for ‘fi’ is something most people never even notice unless it’s pointed out to them, whereas æ and œ are symbols in their own right. Thus, I’m not sure that the Unicode Consortium intends to discourage the use of æ and œ. (Of course, it probably helps that there are languages where they’re required to be written that way, such as French, and even languages where it’s more of a letter than a ligature, such as Danish and Norwegian.)
Of course there are other ligatures but æ and œ are certainly ligatures too in English, Latin, Greek, albeit with special properties. There isn’t a basis to suppose that the standard does not refer to those two ligatures, until it’s stated explicitly. The Unicode guidelines may indeed be discouraging æ et œ ligatures to follow certain modern publishing guidelines which avocate NOT using them in Latin and Greek (Oxford Dictionary for Writers and Editors, 1981, under “diphthongs” and “ligature”, and Hart’s Rules for Compositors and Readers, 1983).
Certè sunt aliae ligaturae. Ligaturae autem quoquè æ et œ, etsi qualitates addititias habent. Sine legibus adversis et explicitis, credendum nobis est ea consilia Unicode omnes ligaturas spectare. Benè possibile est usum latinè graecéque hâc societate æ atque œ ligaturarum deterreri quià deterrent quidem in eis linguis quaedam domus harum dierum editoriae [*].
{*] Vide libros suprà citatos.[/i]
I doubt that has much, if anything, to do with why the Unicode Consortium would discourage the use of æ and œ (if, indeed, they do). It has more to do with separating semantics and presentation; you don’t need a special character for ‘fi’ to display an ‘fi’ ligature, so neither do you need a special character to display an æ ligature.
The main argument in favor of viewing æ and œ as characters rather than ‘mere’ ligatures, I think, would be that it isn’t always correct to make a ligature out of a juxtaposed ‘a’ and ‘e’ (or ‘o’ and ‘e’), only when it represents the Latin etymology. One wouldn’t write “He gœs to the store”, right?
Of course you do. You don’t imagine that a ligature is simply the two separate characters made to overlap. Examine properly designed ligatures closely.
Certè requiris. Noli imaginari ligaturam seu chiro- seu typo-graphicam duas litteras quae inter se simpliciter constrictae sunt. Attentè circumspici ligaturas benè formatas.
Clarification: you don’t need a special codepoint for ‘fi’ to display an ‘fi’ ligature. The font (or typesetting software, or whatever) can handle it for you.
Salvete!
Returning to the original question of when using the ligature:
As this sort of ligature seems to have sprung up in the Middle Ages I had a look at a Neo-Latin text, Topographia Antiquae Romae by Bartolomeo Marliani (my PDF-edition is from 1534 but the “Archive” has ones from 1560). In it I do not see any use of “Æ” even though there are also several upper case-only texts when citing inscriptions (in the transcription of inscriptions he uses, for example, “CAES.”, Marliani uses a lot of the “æ”, but only inside of words, e.g. “Cæesar”, “unaquæque”. On page 55 of my edition it says:
[…]: quorum alterum Sphinga Aegypti peculiare animal.
Nno ligature in “Aegypti” there. Having a quick look I could find only one use of the “æ”-ligature at the beginning of a word, and that would be “æneo” on page 141 (hope I am transcribing this correctly, I am not sure whether the “db” is not some sort of ligature, too):
Ostendit et descripto urbis Romuli a Cor. Tac. db æneo tauri simulacri incœpta.
Another example at the beginning of a section (p. 164, “De Coelio monte, & Coeliolo. CAP. XVIII”) Marliani writes:
COElium montem Querquetulanum prius […]
No use of ligatures in capital letters either. Of course these examples apply only to this particular text, but it should not be too abnormal an example for the typography of that era, should it.
By the way, the “Handbook to Life in Ancient Rome” not even lists these ligatures. The ancient Romans did seem to use quite a few ligatures in inscriptions, but they did not like anything like the “Æ” and “Œ”. Some of them looked rather weird (and seem to have “degenerated” during the later Empire).
Valete,
Carolus Raeticus
Concerning the use of the capitalized ligature Æ before lower-case letters.
For the Romans, there was no rule, no precedent and no practice of using it.
In 16th-century printed books the ligature is introduced for the diphthong (evidence for 15th century?), but it’s optional. You have in English in 1573 Thoman Twyne’s translation of Virgil’s Æneid [N.B.“Æneid”] XII 250, “When forth it bloustringe blowes, and deape Ægæum sea doth raise” (OED under “Aegean”). I see before me in Elisha Coles (A Dictionary English-Latin Latin-English, London 1677) and in Ainsworth (Thesaurus Linguae Latinae Compendiarius, 1808) that Aegyptus and all Latin words beginning AE diphthong have the capitalized ligature Æ before the lowercase letters. From the 16th century, there is a rule (it represents the diphthong), no precedent in the printed page but some in the MSS tradition and some books practice it, some don’t.
In modern works (OED) capital Æ is used for the diphthong at the start of early English words from Latin and Greek retaining the latin spelling, such as Ænigma, Æolian, Æon. Today then, there is a rule (it’s optional for the diphong), there is precedent and there is the custom, though there is some effort to change this (works quoted above).*
_De usum Æ ligaturae majusculae ante litteras minusculas:
- cum Romanis nec ratio monstrat nec auctoritas firmat nec consuetudo clamat;
- cum domibus editoriis post quindecimum saeculum (indicia usûs praecedentia ignoro), ratio monstrat (Æ vel æ loco diphthongi scriptum est vel scribi saltem potest), auctoritas in codicibus antiquis invenitur et consuetudo quorumdam fontium clamat;
- hodiè et ratio monstrat (facultativus est usus), et auctoritas firmat et consuetudo (apud OED in editionibus ante annum mille nongenti sexaginta) usum facultativum clamat, at sunt vestigia mutationis (vide libros suprà citatos)._
- Further the OED now uses the ligature Æ/æ only in this way in English // Porrò anglicè sic hodiè Æ/æ ligatura in OED reperiatur:
"only (1) in Greek and Lat. proper names as in Æneas, Cæsar; even these, when familiar, often take e as Judea, Etna; (2) in words belonging to Roman or Gr. Antiquities as ædile, ægis; (3) in scientific or technical terms as ætiology, æstivation, phænogamous, Athenæum; these also when they become popularized take e, as phenomenon, Lyceum, museum, era.
Æ initial is thus to be looked upon as an earlier spelling of E, and will here occur only (1) in EE. words that became obsolete, before changing to e, as æ law (OE. ), æ river (OE. eá); (2) in words directly adopted or formed from Latin and Greek which became obsolete before changing to e as ædituate; or have not changed to e because they indicate ancient things as ædile, ægis, or are technical as ægilops, ægrotant, ætiology. All other words will be found under their later form in E. "
So // Sicut
NB OLD doesn’t bother at all with that or any ligature, which is ironical but certainly historically justified for classical latin or in any period.
Nota benè, OLD nusquàm eâ vel ullâ ligaturâ utitur, quod ironicum est etsi accuratum praeter consuetudinem classicam vel ullae aetatis!
Salve furrykef
Well, not everyone wants the computer to handle that automatically but OK, I understand it can. But when you say. this:
Non omnis autem id automaticè computatro faceri vult. Verò licet, te intellego. Atqui horum in dicendo:
do you then mean this? // Visne tunc dicere hoc?
Nonnè immò haec: // Do you not mean this?
Theoretically you don’t need a special codepoint for ‘fi’ to display an ‘fi’ ligature because the software could conceivably do that for you, but you need a special codepoint to mark-up an æ ligature because not all “ae” letter combinations are diphthongs.
Theoreticè locus in spatio characterum pro ‘fi’ ligaturâ non requiritur quià programma id pro te facere potest, at requiritur praeter “æ” diphthongum quià non omne illarum litterarum conjugium est diphthongus.
Note however that the software generally couldn’t do it for you unless the original font designer had a code point in Unicode to assign to his or her ligature design in the layout package.
Benè autem nota, non potest ferè programma ordinatrale id facere nisi artifex typographicus jam posuisset formas ligaturarum perfectas in loco spatii characterum Unicode ad usum programmatis componentis.
Note however that the software generally couldn’t do it for you unless the original font designer had a code point in Unicode to assign to his or her ligature design in the layout package.
Private Use Area, my friend. 
The Private Use Area is a range of code points in the Unicode character space unassigned to any specific character. They are still code points. And you still must design special characters to go in them to describe ligatures elsewhere not described. I can’t see the advantage or even the problem you’re addressing.
Regio Usûs Privati pro locibus in spatio characterum Unicode detenta est, qui characteres non aliter definiti sunt. Sunt quidem “loci spatii”. Et oportet characteres proprios fingeri et ad locos designari ut ligaturae non alibi descriptae describantur. Nec quaestionem nec responsum à te tractata non deprendo.
Haha, I have to tell you how much I love you all. This discussion the the best I’ve read since long, and it totally reestablish my faith in the human kind. Latin and comuter geekyness combined must be the best combination ever!
Good word processors (whilst using OpenType Fonts) to some replacement automatically, but you can still have the final say over them. I.e. I can choose some F:s to look on one way, some on another way. You can chose if you want a fi to be a ligature, or if you want it to be two separate letters (which would be good if you were writing Turkish). So if æ were to be a ‹contextual› ligature, then you could indeed chose where it should not be (that or just write aë). No font, however, do have an æ-ligature as a contextual ligature, but only merely as it’s own letter (which Danish, Norwegian, Icelandig and Faroese demands).
Yes, but now they’re an “implementation detail” rather than part of the “interface”, if that makes any sense. Now the codepoints are necessary only because that’s how the fonts work, not because they are inherently necessary to represent ligatures.
Salve furrykef
Not to me anyway, sorry. Maybe it’s all true but it seems a bit vague, especially with speech marks. I don’t know if you’re talking about code points, the Private Use Area, or ligatures, and which interface you are referring to.
Non mihi cognobile est, me ignoscas. Fortassè rectè dicis at confusius id mihi videtur, praesertìm cum notis sermonis. Ignoro an tractas aut de locis, aut de regionibus in spatio Unicode ad usum privatum reservatum, aut de ligaturis, et quam interfaciem referas.
In case I’m misunderstanding you, can you explain how you imagine a ligature is currently created on the computer screen if not from a graphic designed and stored in a font resource file with a Unicode code point as an address? I’m wondering if you think that printing software itself actually creates ligatures from two separate letters.
Ut non plùs te malè intellegem, potesne explicare quomodò computatrum ligaturam in scrinio monstrare credas, si non per locum Unicode numeratum character jam fictus è scapo typorum vocetur? Me rogo an credas programma ad imprimendum ipsum verò è duabus litteris singulis ligaturas fingere.