calligraphist同calligrapher有乜分別?

很少字可以 ist 或 er 都代表人而且意思相同
calligraphy - calligraphist, calligrapher
theology - theologian (神學者,美式), theologist (神學家) 也意思相同

philosophy - philosopher (哲學家), philosophist (虛偽的哲學家; 詭辯家)
physics - physicist (物理學者,唯物論者), physician (醫生,內科醫生)

大多數的字只有一種轉法,而且沒有一定原則.
music - musician
mathematics - mathematician
chiropractic - chiropractor 脊椎治療師
chiropody -chiropodist 腳病醫生
economics - economist
psychology - psychologist
astronomy - astronomer
astrology - astrologer 占星者
chemistry - chemist
history - historian
surgery - surgeon 外科醫生

不能盡錄

calligraphist同calligrapher都係一樣書法家
多數後面ist/er代表人物