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au·thor·i·ta·tive(ə-thôr′ĭ-tā′tĭv, ə-thŏr′-, ô-)
chapter and verse An authority that gives credence and validity to one’s opinions or beliefs; a definitive source that can be specifically cited. The phrase derives from the Scriptures which are arranged in chapters and verses, thus facilitating easy reference to particular lines. In non-Biblical contexts, chapter and verse is frequently a challenge to produce incontrovertible, detailed evidence for one’s opinions. Figurative use dates from the early 17th century.
She can give chapter and verse for her belief. (William Makepeace Thackeray, The Adventures of Philip on His Way Through the World, 1862)
ex cathedra Authoritatively, dogmatically, officially; Latin for ‘from the chair.’ Cathedra itself refers to the chair or seat of a bishop in his church. Most specifically, it refers to that of the Bishop of Rome, the Pope, who according to church doctrine is infallible when speaking ex cathedra since he is not speaking for himself but as the successor and agent of Saint Peter. More generally cathedra means any seat of office or professorial chair. Anyone speaking from such a seat of power or knowledge would naturally speak with great authority. The phrase dates from at least 1635.
from the horse’s mouth On good authority, from a reliable source, directly from someone in the know; often in the phrase straight from the horse’s mouth. The allusion is to the practice of looking at a horse’s teeth to determine its age and condition, rather than relying on the word of a horse trader.
The prospect of getting the true facts—straight, as it were, from the horse’s mouth—held him … fascinated. (P. G. Wodehouse in Strand Magazine, August, 1928)
in black and white In writing or in print—black referring to the ink, white to the paper; certain, verifiable. Written opinion or assertion is assumed to carry more weight than a verbal one. The phrase has been in use since the time of Shakespeare.
Moreover sir, which indeed is not under white and black, this plaintiff here … did call me ass. (Shakespeare, Much Ado About Nothing V, i)