In the English language, we have an alphabet of twenty-six letters. We use these letters to form words and sentences. Each letter is unique; generally, for any given word formed of letters, you can’t substitute other letters without changing the word.
For example, the four-letter word “hose” means something. If you substitute a “p” for the “h,” you get “pose,” which is a totally different word. You can make other one-letter substitutions to get other words, such as “lose,” “home,” “rose,” and “hole.” There is no other way to write these words. There are no other symbols you can use, only the twenty-six unique letters of the alphabet.
Numbers are the exception. (So are a few symbols, such as currency and percent symbols, but I’ll get to that later.)
In English, we can express numbers using words, such as “six” and “one thousand.” But we have an alternative: a parallel system of numerals that mean exactly the same thing as their written versions. These are the familiar Hindu-Arabic numerals in our decimal number system – namely, 0, 1, 2, 3, 4, 5, 6, 7, 8, and 9. They originated in India in the sixth or seventh century and were introduced to Europe through the writings of Middle Eastern mathematicians, especially al-Khwarizmi and al-Kindi, about the twelfth century.
Our use of Hindu-Arabic numerals means that when writers want to include a number in a sentence, they have choice. You can write either “I am fifty years old” or “I am 50 years old.” They both mean exactly the same thing.
When to Use Written Numbers or Numerals
Grammarians love to create rules (or, should we say, order out of chaos), and so every expert has their own rules about when you should write out numbers or use numerals.
There are a few cases where everyone agrees, such as when the written version of a number simply doesn’t exist. These include ZIP codes, phone numbers, and most street addresses. It also includes very large, complex numbers, such as 4,568,780, which no author would write as “four million, five hundred sixty-eight thousand, seven hundred eighty.” Why not? Because it’s ridiculously long, and the reader can’t quickly grasp it. The brain will convert it to numerals anyway, so why not start out that way?
Otherwise there is little agreement.
Most literary authors write out every number, even big ones. They’ll write, “The journey of three thousand six hundred miles took the ship four months to complete.” In dialogue, all numbers are generally written out, to mimic human speech: “The man said, ‘This will cost you five hundred and fifty-three dollars, which you need to pay within twenty-four hours.'”
In non-fiction self-help books, which are much more casual, even small numerals are often used: “If you eat 6 meals a day and ingest no more than 2,600 calories in 24 hours, you will lose 5 pounds every week.”
Business books follow the same pattern, especially when there are lots of numbers that are not “literary” but are more mathematical: “At 4% interest, payments of $25.00 per month over 12 months will lower your balance by only $35.00.”
Note that I’ve also used two of the handful of symbols that in English are interchangeable with a word: “$” for “dollars” and “%” for “percent.” Like numerals, they’re typically used in mass-market self-help and business books, but not in literary works.
What’s the answer? Use your best judgment and know the expectations of your audience!
- Thomas Hauck is a professional author, ghostwriter, and book editor.