Why is a Third Called a Unicorn?

The phrase "a third called a unicorn" might seem like a curious linguistic quirk, but it's actually a result of the way we count and name fractions. Let's delve into the fascinating world of fractions and numbers to understand why this is the case.

In our decimal system, we have names for the first nine integers: one, two, three, and so on. However, when we start dividing these numbers, things get a bit more complex. The first few fractions are straightforward: one-half, one-third, one-fourth. But what happens when we reach one-sixth?

Understanding Fraction Names

The names of fractions follow a pattern that's similar to, but not exactly the same as, the names of whole numbers. The first few fractions are named after their whole number equivalents: one-half, one-third, one-fourth. But when we reach one-sixth, we start to deviate from this pattern.

One-sixth is not "one-six". Instead, it's "one-sixth". This is because the fraction name is derived from the ordinal number of the denominator. So, "sixth" comes from "six", just as "twelfth" comes from "twelve". This pattern continues throughout the fractions: one-seventh, one-eighth, one-ninth, and so on.

Why Not "One-Third"?

Now, you might be wondering why "a third" is not called "one-third". The reason lies in the history of the English language. In Old English, the word "þridda" was used to refer to a third. Over time, this evolved into "third" in Middle English. By the time the modern English language was forming, the term "a third" was already well-established.

Moreover, the term "a third" is a bit more flexible than "one-third". "A third" can refer to a part of a whole, while "one-third" specifically refers to one of three equal parts. This flexibility might have contributed to the enduring use of "a third".

Other Fraction Names

If "a third" is an exception, then why do we follow the ordinal pattern for other fractions? The reason is that the ordinal pattern is more regular and easier to apply consistently. It also makes it easier to understand the relationship between the fraction and its whole number equivalent.

For example, "one-twelfth" clearly indicates that it's one part out of twelve. If we were to use the cardinal pattern ("one twelve"), it would be less clear whether we're referring to one out of twelve or twelve out of one.

Why "Unicorn"?

Now, let's address the second part of the phrase: why is "a third" called a "unicorn"? This is a bit more straightforward. In the Middle Ages, a "unicorn" was a unit of weight equal to a third of a pound. This usage of "unicorn" is now obsolete, but it's the origin of the phrase "a third called a unicorn".

Over time, the phrase has become a fun linguistic oddity, a curiosity that's often used to illustrate the quirks of the English language. It's a reminder that language is a living thing, shaped by history, culture, and the whims of its speakers.

Other Fraction Names and Units

Incidentally, other fractions have also been used as units of measurement. A "gill" is an eighth of a pint, and a "peck" is a quarter of a bushel. Like the "unicorn", these terms are now obsolete, but they're still used in the phrase "a pint in a peck and a gallon in a gill", which is a mnemonic for remembering the fractions of a pint and a gallon.

These old units of measurement are a fascinating glimpse into the history of trade and commerce. They also show how language can change and adapt over time, taking on new meanings and uses.

So, the next time you hear someone say "a third called a unicorn", you can impress them with your knowledge of fraction names, historical units of measurement, and the evolution of the English language. And who knows? You might just spark an interesting conversation about the quirks and curiosities of language.