In the beginning was the Conversation;
and the Conversation was with God,
and the Conversation was God.
- John 1:1, as translated by Erasmus
The Greek word logos (λογος) is notable for its history, for the meanings attached to it by the ancient Greeks (both mystical and mundane), and for its impact on the English language.
The opening of the New Testament's Book of John introduces us to Jesus as Logos incarnate: the Lord's teachings given human form. Logos here has traditionally been translated as the Word (of God), but this is by no means the only meaning of the word, and taken at face value it is at least a little misleading in this context. The word can also can mean reason, thought, or discourse. Desiderius Erasmus translated it as Conversation in his Sixteenth Century rendition of John; but the upper reaches of the church hierarchy were apparently unhappy with this reading, and Word stuck. We can only speculate as to whether it was rejected on theological, political or plain linguistic grounds.
Chinese translations of John often render Logos as Tao, which perhaps captures more of its meaning than any single word in English, besides resonating nicely with Taoist ideas of cosmogony. Like logos, tao can refer to a set of teachings, or to the expression thereof, or to the workings of the universe. While they both carry perfectly everyday meanings, the words are also used in an explicitly mystical sense by many authors - people in a mystic state of oneness with the cosmos are said be communing with the Logos, or the Tao, and although the ancient Greeks and Chinese no doubt conceived of these states differently, there is a strong case for considering mystical traditions everywhere to be centred around a set of analogous experiences.
He arranged in harmonious order this great world, yes, and the little world of man too, body and soul together; and on this many-voiced instrument of the universe He makes music to God, and sings to the human instrument.
- Clement of Alexandria
Another meaning of logos is ratio. The ratios of numbers and of musical tones played a fundamental role in the esoteric mystical tradition originated by Pythagoras, who is credited with discovering the relation between ratios and musical harmony: Ratios were seen as the purest expression of the Logos, conceived of as the ordering principle governing the universe, the numerical reasoning behind all things. This idea of Logos as cosmic rationality was first propounded by Heraclitus, and became a mainstay of Greek philosophy for hundreds of years, especially among the Stoics; the author of John was undoubtedly aware of it, and it is likely that he had it in mind when he chose to refer to Logos rather than rema, which is closer to the meaning of word as in an item of speech.
The interweaving of logical, mathematical thought with mystical, transcendental experience, so characteristic of the Pythagoreans, is seen everywhere in the intellectual and aesthetic traditions of Europe right up until around the start of the Nineteenth Century. The theme of cosmic harmony, and the music of the spheres, crops up again and again throughout the intellectual history of the continent, through Pythagoras to Plato and Cicero, on to early opera and the great alchemist-atronomers Johannes Kepler and Isaac Newton.
People took for granted, by and large, that the principal aim of science, art and religion was to uncover the cosmic order - to comprehend and elucidate the divine mysteries of the universe, and what it means to be human. It is easy to forget just how recently people started seeing any real division, let alone contradiction, between science and logic on the one hand, and religion and spirituality on the other.
'You got an ology! You get an ology, you're a scientist!'
- Maureen Lipman, for British Telecom
Logos gave us the word logic, just as ratio gave us rationality. It has also given us almost every other word in the English language with a log in it (besides the odd exception like log itself) - the -ology words, which most often refer to a set of teachings, sometimes a science (physiology, psychology, astrology et al); the -logue words, usually something to do with speaking, sometimes in a roundabout sort of way (monologue, dialogue, catalogue, etc.); and the logo- words, which are typically words about words (logodaedaly, logorrhea, logology and so on). Logo, one of the more obvious derivates of logos, is probably a shortening of logogram, literally 'a word as it is written', and hence a sign representing a word.
The word logos seems to have descended from a proto-Indo-European root leg, meaning 'to collect', presumably in the sense of picking out words to speak; the same root, by other routes, has given us collect, legend, lexicon, and so on.
Logos itself has been adopted into modern English, initially to cover its ancient Greek meanings which are not carried over into English words like 'word': People discussing the book of John, and works (like those of Clement of Alexandria) which draw on it heavily, frequently use logos to make clear that they are not talking about 'the word' or 'reason' in any modern sense. Logos was also used by Jacques Derrida and Carl Jung to refer to fairly specific concepts, while English-speaking mystics of the present day have been known to use it to refer in an abstract way to the world of thought, and to the universe as information.