Etymology is a tricky business that shouldn’t be entered into by folks without the proper background. That’s when you get what’s called ‘folk etymology.’ Folk etymology can be very instructive for the history of words, especially as it tells us about the attitudes and perceptions of people at various periods, but studying folk etymology is a very different thing from creating it, which is at the heart of a great deal of bad scholarship in the novelty-hunting tradition. Along with folk etymology, such scholars are prone to pull indiscriminately from multiple fields, from vastly different cultures, and to cherry pick data while variously overwhelming their audience with unverifiable facts and withholding information that would reveal the weakness of both their argument and their command of the material.
Somehow I stumbled onto the Latin names for the fingers, and wondered about the origin of the phrase digitus medicinalis or digitus medicus. I had a thought as to the origin of the term, which I’ll come back to at the end, but I did a quick search to see what the internet had to say.
The Wikipedia page for the ring finger links to a dubious article on the etymology of the term. The author, László A. Magyar, never makes a coherent argument about what he claims is the predominant association of the ring finger in ancient cultures, namely magic, but tries to seal this conclusion with the following (which I quote at length):
Before drawing conclusions, let us examine the name digitus medicinalis itself. The adjective medicinalis originates from the werb medeor (medico), the original meaning of which is not else than «to heal by magic » (26). The werb can be traced back to the stem med (27) – this stem designates «middle» – that is how perhaps the original meaning of the word medicus, i.e. «mediator» (medium), a mediator between humans and the world of spirits (i.e. magician) can be interpreted. That this is not only a mere brain wave is proved not only by a line of Silius Italicus, naming magicians medicum vulgus (28), but also by series of linguistic parallels, too (e.g. in German the word Arzt has originally meant also magician, while the Greek iatros derives form iaino of similar connotations (29).
In conclusion, the following statements can be made: based on linguistic and ethnographic examples, it seems to be evident that the ring finger is a finger of magic power. It appears to be sure that the ring-finger names almost always indicate the magic power of the finger: in this respect, according to our assumption, the Latin digitus medicinalis is not an exception either, since according to its original meaning, it is more correct to translate this expression not as «medical» but as «magic» finger. So Galen was wrong this time: the ring finger received this peculiar name not from the physicians but from the most: ancient way of healing, i.e. magic (30). Consequently, in the name digitus medicinalis the ancient meaning of the word medicinalis can be detected, this being none else than «magic».
The bold assertion that ‘Galen was wrong’ is unfounded for a number of reasons, not least because he’s not even talking about Galen.
But first, his etymological game is beyond weak. The roots in words like medicus (from P.I.E. *med-, ‘to take appropriate measure’), medius (from P.I.E. *medhyo-, ‘middle’), and magus (from P.I.E. *magh-, ‘to be able, to have power’) are unrelated and unlikely to have been confused in antiquity. Loose semantic associations without a whit of evidence can not make up for the failures of such a phonetically-based pseudo-etymology.
But as I said, he’s not referring to Galen, but to a work commonly known as Introductio sive Medicus by Ps.-Galen, and here’s the passage in question:
δακτύλων δὲ ὁ μὲν μέγιστος ἀντίχειρ καλεῖται, διὰ τὸ ὅλῃ τῇ χειρὶ ἄκρᾳ συνεργοῦντα ἴσον αὐτῇ δύνασθαι. ὁ δὲ μετὰ τοῦτον λιχανὸς, ὡς ἔοικεν, ἀπὸ τῆς χρείας τοὔνομα ἔχων· ἐφεξῆς ὁ μέσος καὶ μετὰ τοῦτον ὁ παραμέσος, ὁ τοῖς ἰατροῖς ἀνακείμενος καὶ ἀπ’ αὐτῶν τοὔνομα κεκληρωμένος. ὁ δὲ ἐπὶ πᾶσι μικρὸς, καθ’ ὃ πάντων ἠλάττωται.
This says that the largest of the fingers is called the ‘anti-hand’ because it works opposite the rest of the hand (the ‘opposable thumb,’ of course), that the next is called the ‘licking’ finger from its use (as the tongue of the hand? ‘licking’ things up?), then comes the ‘middle,’ then the ‘next-to-the-middle’, which is dedicated to doctors and has gotten its name from them, and finally the finger after all the others, which is the ‘small’ finger according to its being smaller than all of them (naturally enough).
What’s odd is that the author calls this finger the ‘next-to-the-middle’ and not ‘the medical finger.’ Still, he seems to have felt the need to follow-up with an explanation of this or some similar term which must have been relatively common. What’s interesting to me is that someone writing a medical book seems to have understood the connection to physicians. What might it have been?
So now we come to my initial guess. If you’re a woman, or if you’ve seen a woman apply make-up or (more probably) eye cream, you may know: the ring finger is supposed to have the softest touch.
I think there’s more to it than that. The ring finger is less independent. You’re more likely to make small, sharp movements with your index finger, and to bend your finger, not only pulling skin but scratching yourself and getting makeup or cream under your nails. By using the ring finger you force an effect similar to holding a pencil for drawing as opposed to writing: now the motion is controlled less by your finger (or hand) and more by your arm. It’s counterintuitive, but this allows for smoother, more careful application.
I imagined a doctor applying medicine in just this way when I first encountered the Latin phrase. It has the added benefit of keeping the index finger free and clean for performing other tasks or holding implements, etc.
The oldest reference to the digitus medicus that I can find is in Pliny the Elder who gives the following among supposed remedies for boils (at XXX.34):
muscae impari numero infricatae digito medico
Why anyone should rub an uneven number of flies on a boil using their ring finger is beyond me, except for the fact that the ring finger again has the lightest touch and might aid in the careful application of the ‘medicine.’
Other suggestions? J. Hilton Turner in the Classical Journal of November 1951 explains in a footnote that it “seems to have come from the practice on the part of doctors of using this finger in conjunction with the thumb to lift pinches of various materials.” His citation is unavailable to me, but it makes sense too.
How does this differ from folk etymology? Well, whereas Magyar invented linguistic connections that weren’t there to fit a novel and desired result (i.e., that the ring finger was magical), I’ve said nothing about the ‘true origin’ or the ‘secret history’ of the word, but simply looked for an explanation for the actual usage.