Imam al-Ghazālī on Specialized Expertise

"A person skilled one one field is not necessarily skilled in every field. Thus a man skilled in jurisprudence and kalām is not necessarily skilled in medicine, nor is a man who is ignorant of the speculative and rational sciences necessarily ignorant of the science of syntax. On the contrary, in each field there are men who have reached in it a certain degree of skill and preeminence, although they may be quite stupid and ignorant about other things."

-Al-Ghazālī, Deliverer from Error, p. 32.