The Grammarphobia Blog

An inflammatory question

Q: I hear people using the words “flammable” and “inflammable” to mean the same thing—easily burnable. Shouldn’t “flammable” mean burnable and “inflammable” mean not burnable? It doesn’t make sense to me. Help, please!

A: Historically, both “flammable” and “inflammable” have meant the same thing, easily ignited and capable of burning rapidly. “Inflammable” is by far the older word, dating back to at least 1605, according to the Oxford English Dictionary. “Flammable,” the new kid on the block, didn’t appear in print until more than 300 years later.

The cause of all the confusion is the “in” at the beginning of “inflammable.” As it turns out, “in” can be either a negative prefix or an intensive prefix (one that shows increased emphasis). It’s negative in words like “incapable” or “inflexible,” while it’s an intensifier in words like “inflate” or “inflame” or “inflammatory.”

Here’s the history. “Inflammable” comes from the Latin “inflammare,” meaning to inflame, while “flammable” comes from the Latin “flammare, which means to set on fire. The word “flammable” was coined in the early 19th century, but it was rarely used for decades, according to The Mavens’ Word of the Day, a Random House website.

Insurers and scientists revived “flammable” in the early 20th century as a replacement for “inflammable,” which was considered confusing because of that two-faced “in” at the beginning. After World War II, the British Standards Institution took up the campaign, encouraging the use of “flammable” vs. “non-flammable” rather than “inflammable” vs. “non-inflammable,” according to the Random House website.

So which word should a careful writer use today? The American Heritage Book of English Usage recommends going with “flammable” when clarity is important, such as in warning signs. I second that opinion.

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