Usage of -ist and -ian, when to use which?

This is a question bugging me for a long long time, especially for a non-native speaker like myself.

We have physicist standing for the people doing physics research, as is linguist, chemist, etc.

But for math, the counterpart of "-ist" suddenly becomes "-ian": I call myself a mathematician.

What bugs even more is that we have physician as well, yet representing a totally different occupation with physicist.

This is not the end, in mathematics, we have so many adjectives derived from the names of mathematicians. Through some wikipedia-fu I learned they are called eponymous adjectives, most of which I used often end with "-ian": Newtonian potential, Cartesian coordinate system, Lorentzian transformation etc. These words often indicate somewhat the relationship of possession.

Yet again, not all possessive relations are represented using "-ian", there are: Maxwell's equations, not Maxwellian equations; Gauss's divergence law, not Gaussian law (even though there are tons of things with Gaussian in it).

What confuses me even more, is that "-ian" after people's name can not only represent "of someone", it also can stand for "a believer or supporter of someone's theory". For example, I call myself a Kantian. There is Leibnizian as well, the supporter of Leibniz's philosophy.

Now my questions are:

• Is there a standard rule to decide which one to use, "-ian" or "-ist", when describing an occupation?

• For eponymous adjectives, my vague impression is that: when something is derived not by that specific person, but rather whose derivation bears the spirit of that someone's theory, then we use "-ian". For example, Newtonian potential is not invented by Newton, yet Maxwell's equations are unified by Maxwell. But another example is that Descartes invented Cartesian coordinate system, but the system is not called Descartes' coordinate system...How to tell if we want to invent some new terms? For example, if I proved a new theorem using some idea from Newton, do I call the proof Newton's argument or Newtonian argument?

• Can "-ian" be used interchangeably in "I am a Kantian" and "This is a Kantian style argument."? or there is some tradition for each word ending with "-ian"? i.e., Some words ending with "-ian" can be only used as noun or adj.

Solution 1:

Is there a standard rule to decide which one to use, "-ian" or "-ist", when describing an occupation?

The suffix in mathematician and physician (and other words such as politician, magician) is actually -ician (from the French -icien) which is constructed by taking the suffix -ica (names of arts or sciences in Latin such as: magica, mathematica, politica etc) and "adding" -ian to the -ica suffix (I write "adding" because the "a" is dropped from -ica):

magica -> mag-ica -> mag-ic(a)-ian.

So, the suffix -ician means someone who is a specialist or practitioner.

(Also the -ician rule also sometimes - confusingly though, not always - applies to such words which don't end in -ica but instead just -ic, such as: academic becomes academ-ic -> academ-ician and the same for geometr-ic: geometr-ician.)

As for the specialist words ending with -ist (linguist, chemist), I am not sure, but I think the Latin word stems for these words end in just -a rather than -ica: chemista (chimista?) and lingua. I think these -a word stems get the -ist suffix, from the French -iste or Latin -ista. (agential suffix)

How to tell if we want to invent some new terms? For example, if I proved a new theorem using some idea from Newton, do I call the proof Newton's argument or Newtonian argument? [...] Can "-ian" be used interchangeably in "I am a Kantian" and "This is a Kantian style argument."? or there is some tradition for each word ending with "-ian"? i.e., Some words ending with "-ian" can be only used as noun or adj.

Here I am not as sure. The suffix -an means "pertaining to," from Latin -anus, in some cases via French -ain, -en. I cannot explain the added "i" in Newton-i-an. Maybe it is added to make the word sound better than just "Newtonan".

Solution 2:

There are likely several factors that determine the choice between the two suffixes -ian and -ist. Some of these, such as the word root and the resulting sound, have already been mentioned. Another one is a slight difference in meaning: both tend to convey the notion of expertise. The difference is that -ian tends to communicate something more comprehensive, while -ist has a more narrow focus. E.g. musician but violinist, pianist, flutist, cellist; Physician (general practitioner) but cardiologist, dermatologist, gynecologist, dentist. Academician but linguist, botanist, geologist, biologist, chemist, physicist, economist,

The narrowing of focus can sometimes take on a negative connotation as it does in racist, sexist, as well as fascist, communist, capitalist and anarchist as opposed to the more positive connotation of libertarian and humanitarian. A Kantian or Marxian is someone who is knowledgeable about and influenced by Kant or Marx, while a Kantist or Marxist would be a strict follower, blind to alternatives.