Homo unius libri

Homo unius libri is a Latin phrase attributed to Thomas Aquinas by bishop Jeremy Taylor, who claimed that Aquinas is reputed to have employed the phrase "hominem unius libri timeo".
The poet Robert Southey recalled the tradition in which the quotation became embedded:
The phrase was in origin a dismissal of eclecticism, i.e. the "fear" is of the formidable intellectual opponent who has dedicated himself to and become a master in a single chosen discipline. In this first sense, the phrase was invoked by Methodist founder John Wesley to refer to himself, with "one book" taken to mean the Bible. However, the phrase today most often refers to the interpretation of expressing "fear" of an ignorant person who has "only read a single book".