Why "paediatrics" but "pedagogue" in British English?

Question

There's an account of the British ae/oe and American "e" spellings (as in diarrh(o)ea, f(a)eces, and other fun words) on wikipedia.

What I'm wondering is why, even in British English, pedagogue/pedagogy etc. lose the "a", despite coming from the same "paid-" root as e.g. paediatrics.

I've checked the OED, and the ped- spelling seems to consistently predate paed- - as in e.g. Pedocracy (1647) and Paedocracy (2000). Here, for those who have access.

So, can anyone:

• shed any light as to why/when/how British English regained that lost vowel in all other ae/oe words than pedagog-?
• and/or suggest other words with similar behaviour in British English?

UPDATE: to clarify, the question put more technically is: what is the basis for some words containing what were originally Ancient Greek diphthongs oi/ai coming into the language informally referred to as British English written with just an "e" and not ae/oe?

Answer 1

pedagogue is mostly from French, paediatrics is mostly from Latin

Well, as the OED says, although the word pedagogue comes from Greek if you go back far enough, the immediate sources of the English word are French and Latin. (You can see the French influence on the spelling in the use of -gue to represent a hard g sound.) In fact, with the exception of the acute accent, the French word pédagogue is spelled identically to the English word pedagogue.

This suggests to me that when the word entered Middle English, it was basically a borrowing from French, and so started out with the French spelling. Later on, as it became more established as an English word, the French spelling became less relevant, but the Latin/Greek origin was still obvious. So people began using the ae spelling that more closely corresponds to the Greek etymology.

The word p(a)ediatrics is more recent and also more clearly derived directly from Latin (from words like paediatria and paediatricus/-ica). A French form pédiatrique is attested as having some use in the OED, but it clearly did not win out.

Edit: the pronunciation probably influenced the modern spelling

Chris suggested in a comment here that the spelling might be connected to the pronunciation. Although I initially did not think this was true, I now have found some evidence that caused me to change my mind. It seems to be pretty rare in British English for the digraphs ae and oe to be pronounced as lax /ɛ/. Most apparent counterexamples I first thought of, such as aesthetics, anaesthetize and diaeresis, seem to have variant pronunciations with /iː/ that are used in British English. (And see the comment here by a British speaker: “Oestrogen” and “oesophagus” — why are they spelled differently in British English?) If the spelling ae has come to be strongly associated with the sound /iː/ in British English, this might provide a reason why British people came to prefer the spelling pedagogue.

Similar words:

• heretic, heresy, which also have lax e in the first syllable. Heretic ultimately comes from Latin haereticus, but like pedagogue it entered English through French (hérétique) and the earliest spellings in English used simple e, according to the Oxford English Dictionary (for example, eretik(e), heretyk(e), heretike). The OED also records some variant spellings with ae such as hæretik, hæretick(e), hæretique but they are no longer used.
• spherical is also traditionally pronounced with lax e, even though its Latin ancestor sphaericus has ae, and the spelling variant sphærical which was used at some points in the past has not survived. (The earliest forms of this word are spelled with "e" and start with "sp," like "sperycall.") Of course, the corresponding noun sphere has tense e and is also spelled with the single vowel letter "e," which is another reason that we wouldn't expect spherical to be spelled with ae, regardless of the pronunciation.
• pre-: this prefix comes from Latin prae-, but it is never spelled that way in modern English. These spellings have occasionally been used in the past, though, like praelude and praesident. It is generally pronounced as /priː/, but there are some words where it represents /prɛ/.

Answer 2

Language is a fluid beast and words come into it from a number of sources and sometimes a choice is made as to which version is to be used or, due to a lack of similar phonemes, a compromise is made - for example, borscht is taken from the Slavic борщ which would transliterate as borshch.

As noted above, both pedagogue and paediatrician come to us from Greek (the root παĩς - pais or paedion - which means child) but via different routes.

Pedagogue comes via Latin - which is where we get the dipthong ae - to French - which is where ae changes to é. We have no é in English, so we get a regular e.

Paediatrician has come to us straight from the Latin, which took it from the Greek. Note paediatrician in French is pédiatre.

Why there is a preference to take one version over another is a question I am not sure anyone can really answer.

It is possible that French was more fashionable to use at any given time; Greek to Latin was seen as more scientific, perhaps, or maybe the writers of a dictionary in any given year that a word became accepted, decided they liked the look of one spelling over another.

@EdwinAshworth American English is certainly not ill-defined - it is the version of English that began with the work of Noah Webster, soon after the War of Independence who, depending on the version you want to believe, wanted to either make spelling simpler or move away from the British version of words (American English changes in spelling are often taking Greek versions, rather than French) or a bit of both. It was then continued by organisations like the American Philological Association.

Similarly, British English is what is used in the UK and the rest of the English speaking world.