What happens when you come across a word you don’t know? Do you just keep reading? Most people do. They believe they can figure out a word’s meaning by looking at the sentence and using common sense. Maybe they’re right … but what if they’re wrong?

Here is a passage from a profile of a historical figure: “The prince, once a redoubtable opponent, became enervated by constant warfare.”

Choose which of the following sentences is true of the prince:

• The prince was a mighty warrior at first, but constant warfare exhausted him.
• The prince was not much of a soldier at first, but constant warfare made him a mighty warrior.

Those who cannot be bothered to look up redoubtable and enervated risk going through the entire essay with a distorted impression of the prince. Such readers are just wasting time—theirs and the author’s.

Serious readers look up every word they don’t know, even words they’ve seen before but are a bit fuzzy about. It is astonishing how few people demand this of themselves. Looking up a word never enters their minds, even though doing so takes mere seconds nowadays.

According to the language scholar Charles Harrington Elster, the average educated adult American has a vocabulary of between twenty-five thousand and forty thousand words. The Oxford English Dictionary contains more than six hundred thousand words—more words than exist in French and German combined.

So even if you had three times the vocabulary of the average person, you still would only know one out of every six English words that have ever appeared in print.

Last week’s article included a sentence that prompted a surprising reaction. We wrote: “Then there are those Wall Street peculators whose malfeasance still has the country reeling.” Some readers assumed we meant “speculators.” Their emails ranged from civil to scornful. One correspondent simply sent us the offending sentence, with “peculators” blown up to three times the size of the other words. This is the verbal equivalent of rubbing a naughty puppy’s nose in the mess he’s made.

It is beyond us why anyone would write a “gotcha” email before doing basic research. If you type peculate into a search engine you’ll get the definition in a few seconds. It probably took longer for the puppy-shamer to enlarge “peculators” than it would have taken him to look it up.

Speculating is legal; peculating is a crime. “Speculators” was too mild for our purposes. To us, “peculators” was le mot juste.

So exercise due diligence before you hit “send,” or the mistake you expose may be your own.