“In the dark” is an idiomatic expression that means someone doesn’t know about something. The phrase implies that the person is unable to see the truth or the information, as if they were in a dark room. It may refer to one person keeping information from another, or to ignorance of something. An idiom is a figure of speech whose meaning is different than the actual words, yet explains the concept through comparison.
When someone is in the dark about something, they lack information about it. This idiom can be used to refer to a person who has no knowledge of a particular topic or incident through ignorance. For example, “Bob was in the dark about auto mechanics, so he couldn’t fix his car.” The expression may also mean that someone else is withholding information or being secretive, as in “The boss kept employees in the dark about the recent merger until it was completed.”
An idiom has a figurative meaning that is different from the actual words and phrases included. No one actually turns out the lights on someone to keep them from the truth. In a room or place without light, nothing can be seen, and thus the implication of blindness to an issue is implied. Idioms have traditionally been a part of informal speech, but many phrases in popular communication have found their way into the dictionary.
“In the dark” as a phrase has been known since the 1600s. Idioms fall in and out of fashion, but their meaning changes very little over time. A simple expression like this one explains a concept in far less words than a literal phrase would. Writers can use idioms to establish a sense of time and place in a novel, story, or film because their usage varies depending on the time period and references involved.
Idiomatic expressions are reflections not of language, but of culture. For example, une faim de loup in French literally translates to “hunger of a wolf,” meaning a great and ravenous appetite. Although most English speakers would understand that particular idiom, the cultural origin may be lost on them. In France alone between the 1500s and the 1800s, wolves did attack people and were greatly feared, so the comparison between a very hungry person and the animal is apt. Non-native students learning a language need to study its idiomatic expressions in order to fully understand native speakers.