As far as I know, the word “aesthetic” can be considered the “British” or “European” way of spelling the word, like “caesium” or “haemophilia”. The spelling “esthetic” (which replaces the ae with e as so many American spellings of those words do) does exist, but I’ve barely ever seen it written that way anywhere. Do Americans also typically use “aesthetic”? If so, how come?
It is true as a general rule, that with words that contain an ae or oe originating from a dipthong of Latin or Greek origin (rather than from a compound of a word ending in a or o and one beginning with e, or from the letter æ as used in some Germanic languages), then:
- You will most likely find the spelling to be ae or oe in some forms of English, including British, and Irish English.
- You will most likely find the spelling to be e in some other forms of English, including American and (to a lesser extent) Canadian.
- You will most likely not find the spelling to be æ or œ any later than the early twentieth century, though it does still occur in some idiolectic orthographies (hey, some of us just think it reads nicer).
Famously, moving toward the simpler e was one of Webster’s spelling reforms, which as a rule were more popular in the US than elsewhere (though neither fully accepted there, nor fully rejected elsewhere), but those forms were found before his time, and he settled on them as the preference rather than inventing them.
There are though a few exceptions.
In one direction you’ve noticed that aesthetic is more common than esthetic as a spelling of æsthetic, even in the US.
Just why is hard to say, though probably a factor is that moving toward esthetic would change the beginning of the word, and so be a strong change in people’s minds (and so less likely to seem “natural”) and affect where it was found in the dictionary. Likewise, oenology is more common than enology in the Americas.
Conversely, fœderal and foederal are pretty much dead, being replaced by federal in British as well as American English. Likely this owes something to fact that the term federal is of such import in American politics and fœderal has not seen much currency in British politics since the Treaty of Union of 1706 and Acts of Union 1707, during which time the term fœderal union was a popular description of the proposed new Kingdom of Great Britain: When those of us in Britain and Ireland hear about “federal government” it is most often in the context of American matters. (Australians also have a federal rather than foederal government, foederal had already died out by the foundation of the Federation of Australia).
In the middle, fetus will be found alongside foetus and fœtus in Britain (foetus and fœtal are a hypercorrection anyway, as the original Latin was fetus though the other forms started popping up in Latin texts around the 16th Century), and likewise homeopathy for homoeopathy or homœopathy, and medieval for mediaeval or mediæval can be found in Britain. Conversely archaeology is found in the US outnumbering archeology.
The reasons are various and often hard to trace. In some cases a standard may have an effect cesium is most common in the Americas, but some scientiest use caesium as the IUPAC-recommended spelling. In some cases it’s a matter of who one sees writing of a particular topic the most; there is after all commerce of ideas between the English-speaking countries. In many cases, it’s really hard to say just why a form became preferred where it bucks the general trend.
Classical names are generally in the longer form, such as Caesar, while current names in the form used by their personal or corporate owner; hence Encyclopædia Britannica, World Book Encyclopedia and Chambers’s Encyclopaedia so as to remain faithful to what is seen as the proper form of the word in each case, under the general rule that one should avoid orthographic damage to someone’s name.