Is a Thumb a Finger? What Anatomy and Dictionaries Say

Is a thumb a finger?

Is a thumb a finger? The answer depends on which meaning of finger you use, and English has two. In the broad sense, a finger is any of the five digits at the end of your hand, thumb included. In the narrow sense, the fingers are the four long ones, and the thumb is its own thing.

Both senses are in everyday use, which is why this argument never ends at the dinner table. Ask people how many fingers they have and most say ten. Ask them to point with a finger and nobody uses a thumb.

What dictionaries say

Dictionaries record both senses, and they lean narrow. Dictionary.com defines a finger as any of the terminal members of the hand, especially one other than the thumb, and its plain English note says you have four fingers on each hand, or five if you count the thumb. Oxford Learner's Dictionaries describes a finger as one of the four long, thin parts of the hand, adding that the count is five if the thumb is included.

Notice the word especially. It makes the narrow sense the default, not the only meaning. The thumb is not shut out of fingerhood; it is just not what people usually mean when they say the fingers.

The verdict

What it sounds like

What anatomy says about the thumb

Anatomy gives the no side its best arguments. According to Cleveland Clinic, each finger has three small bones called phalanges, while the thumb has two. The thumb is also the only digit that can oppose the other four, and Cleveland Clinic describes the precision grip, the move you use to pick up a pen or turn a key, as your fingers meeting your thumb.

It even has its own name and its own muscles. Anatomists call it the pollex, and the thenar muscles at the base of your thumb, the bulge in your palm, exist to control it.

But anatomy also files the thumb with the others. It is listed as the first digit of the hand, its segments are phalanges like every finger's, and Cleveland Clinic's page on broken fingers covers broken thumbs too. So anatomy does not say a thumb is not a finger. It says the thumb is a digit with differences that matter to doctors and surgeons.

How everyday English and music count it

Everyday phrases often keep the thumb separate. If you are all fingers and thumbs, you are clumsy with your hands; Oxford lists the idiom as be all fingers and thumbs, or just be all thumbs. A rule of thumb and a green thumb need no finger at all.

Music shows both sides in one history. In modern keyboard fingering, the fingers of each hand are numbered 1 to 5, and the thumb is 1. But in 19th century Britain, the so-called English fingering marked the thumb with a cross or a zero and numbered only the other four, 1 to 4. Piano teachers have been on both sides of this debate.

Why this argument never ends

Both people are usually right about different things. The yes side is using the broad meaning, and the no side is using the narrow one. Arguing past each other with one word in two senses is equivocation, and it powers most of the classic definition debates, from whether water is wet to whether a hot dog is a sandwich.

The fix is to agree on the question first. Are you asking how English works, how a hand works, or who owes whom five dollars? Each has a slightly different answer, and naming which one you mean ends most of the shouting.

The ruling

A thumb is a finger, but not one of the fingers. In the broad sense that dictionaries allow, your thumb counts, so ten fingers is a correct answer. In the narrow sense English uses by default, and in anatomy, the thumb is a distinct digit with two bones, its own muscles and a job no other finger can do.

For bets: if the question was whether a thumb is a finger, pay the yes side. If it was whether a thumb is just like the other fingers, the no side wins. Still deadlocked? Put both sides into the argument judge.