We prefer to think that the absence of inverted commas guarantees the originality of a thought, whereas it may be merely that the utterer has forgotten its source. – Clifton Fadiman, The American Treasury, 1455-1955, 1955
But further, in order to embellish it with flowers of language and gems of thought, it is not necessary for this ornamentation to be spread evenly over the entire speech, but it must be so distributed that there may be brilliant jewels placed at various points as a sort of decoration. – Cicero, De oratore

