 By a “description” Russell means any phrase of the form “a so-and-so” (an “ambiguous” or “indefinite” description) or “the so-and-so” (a “definite” description), though he focuses on the latter in his discussion of knowledge by description. Russell’s definition of knowledge by description builds naturally on this: To know some thing or object by a definite description is to know that it is the so-and-so or that the so-and-so exists, i.e., that there is exactly one object that is so-and-so (Russell 1912: 82–3). On Russell’s view, proper nouns, and most common words, are really disguised descriptions (1912: 84–5). We might claim to know who Jack the Ripper was, that he was a vicious human being, and so on, but we can only think of and know the individual about whom the claim is made through a description of that individual—Jack the Ripper is that person (whoever he was) who committed certain atrocities in London in 1888. We have no “first hand” knowledge of the person about whom our judgment is made—we don’t even have “first hand” knowledge that only one individual committed the murders or, for that matter, that the murders took place. Put another way, we are not directly acquainted with either the crimes or the perpetrator of those crimes since he is long dead and we have surely never met him.