Joshua Trachtenberg, Jewish Magic and Superstition, 1939:

The essential character of things and of men resides in their names. Therefore to know a name is to be privy to the secret of its owner's being, and master of his fate. The members of many primitive tribes have two names, one for public use, the other jealously concealed, known only to the man who bears it. Even the immediate members of the family never learn what it is; if an enemy should discover it, its bearer's life is forfeit. In highest antiquity and in our own day, among the most primitive and the most civilized peoples, the occult power that inheres in the name is recognized, and the name itself is known to be a mighty and awesome force in the hands of the magician.

To know the name of a man is to exercise power over him alone; to know the name of a higher, supernatural being is to dominate the entire province over which that being presides.

Henry Cornelius Agrippa, Three Books of Occult Philosophy, 1651:

That proper names of things are very necessary in Magicall operations, almost all men testifie: For the naturall power of things proceeds first from the objects to the senses, and then from these to the imagination, and from this to the mind, in which it is first conceived, and then is expressed by voices, and words. The Platonists therefore say, that in this very voice, or word, or name framed, with its Articles, that the power of the thing as it were some kind of life, lies under the form of the signification.

Sir James George Frazer, The Golden Bough: a study of magic and religion, 1890:

Unable to discriminate clearly between words and things, the savage commonly fancies that the link between a name and the person or thing denominated by it is not a mere arbitrary and ideal association, but a real and substantial bond which unites the two in such a way that magic may be wrought on a man just as easily through his name as through his hair, his nails, or any other material part of his person. In fact, primitive man regards his name as a vital portion of himself and takes care of it accordingly. [...]

We are told that the secrecy with which among the Australian aborigines personal names are often kept from general knowledge 'arises in great measure from the belief that an enemy, who knows your name, has in it something which he can use magically to your detriment.'

Donald Mackenzie, Egyptian Myth and Legend, 1907

The Ran, or name, was also a manifestation of the Ka [spirit]. Power could be exercised by uttering the name, because there was magical influence in those words which were believed to have spiritual "doubles". A personal name was the spirit identified; its service was secured when the name was uttered. The spirit was the name and the name was the spirit. If a magician desired to work evil against an individual, he made use of the name when uttering potent magical formulae. The dead were similarly conjured up when their names were spoken in invocations; evil spirits were cast out by those who knew their names. To guard himself against wizards who uttered "words of power", or verbal spells, the Egyptian therefore considered it necessary to have two names--the big name and the little name, or the true name and the good name. He kept his "big, true name" secret, because it was the Ran; his "good little name" was his nickname, and was not a part of his living being.