Views
Because of its poetic virtues, for centuries the eye has served for lyrical comparisons and for allegories. One cannot, even summarily, compile a list of the writers who have found an analogy between it and the stars. In metallurgy it tends to be regarded as a cavity, a hole: the eye of a crankshaft, eyelet (of a shoe). Then, by extension to the technique of the arts, people have spoken of l'oeil d'une oeuvre (the eye, thus the look, of a work) in the sense of appearance. Hence the expression tu en as un oeil, you're looking good. Argot, that poetic language, rich in poetic imagery, and accursed, has naturally made much use of the organ of sight: le quart d'oeil (commissariat of police) derives – and in the process outdoes it – from the classical proverb ne dormir que d'un oeil, comme le gendarme (to sleep with one eye open, like a policeman). Coco bel oeil, which has passed from slang into polite usage, with a certain old-fashioned military whiff about it, alludes less to the organ of sight than to one of its functions, l'oeillade, the amorous glance or ogle. The eye's fragility quickly led to its being made a term of comparison with something precious: j'y tiens comme à la prunelle de mon oeil, I treasure it/him/her like the apple of my eye; then again, by extension, as a sensitive spot not to be touched without good reason, as it emerges from the very formula of lynch law, oeil pour oeil, an eye for an eye. One could hold forth as lengthily on the numerous obscene senses of the word, brought about by its analogy with the private parts: mon oeil, crever l'oeil, and the famous mettre le doigt dans l'oeil (to poke one's finger in one's eye), which, taken initially in a figurative sense to express a concrete action, has been taken up again in the proper sense to express an abstract state (to be mistaken, to make a blunder) admirable ideo-material property of the senses.
The expression à l'oeil, free, gratis, is the paraphrase of a medieval story in which a poor wretch who having eaten the smell of a roast, pays with the sound of his money; hearing, by way of cash, having been replaced by sight.
Pour vos beaux yeux, for your beautiful eyes, was originally a knightly expression. It was rightly estimated that the quality of beautiful eyes was enough to pursue dangerous adventures. It is the debasement of the ethics of love in connection with the evolution of customs which makes it possible today – when "dispassionate" people (in both the exact and the figurate sense) consider love to be a trifle – to confuse cause with effect, to be of the opinion the mourir pour beaux yeux, to die for beautiful eyes, is not an enviable fate.
Ouvrir L'oeil et le bon, literally to open one's best eye, meaning to be on the look-out, to keep a weather eye open, takes us back to the vocabulary of the gendarme. It nonetheless has a scientific justification, since it is rare for a man to have the same acuity of vision in each eye. However there is no doubt an allusion here to the need for a marksman who wishes to aim straight to shut one of his eyes. So it would surely be better to say fermer l'oeil et le mauvais (close your worst eye).
Finally we shift the whole to the part, and the words prunelles, pupils, cils, lashes, orbites, sockets, paupières, eyelids, have entered ordinary language and enriched the figurative vocabulary: froncer les sourcils, to knit the brows, to frown, jeter un cil (flick an eyelash), to have a peep, se mirer dans des prunelles, to gaze into someone's eyes, etc., before themselves falling into popular usage.