Keep someone posted is an idiom with uncertain origins. An idiom is a figure of speech that is a word, group of words or phrase that has a figurative meaning that is not easily deduced from its literal definition. We will examine the definition of the phrase keep someone posted, some theories as to where it came from and a few examples of its use in sentences.
To keep someone posted means to keep someone informed, to supply someone with constantly current information. The origin of the expression to keep someone posted is lost in the mists of time. It may have come from the verb to post meaning to nail public documents and information to a wooden post in the public square, a common practice in the Middle Ages. Another possibility is the use of the word post to mean mail. The original mail systems consisted of horse riders stationed or posted along a route. In either case, the idea is the sharing of current and pertinent information. Keep someone posted is a verbal phrase, related phrases are keeps someone posted, kept someone posted, keeping someone posted.
He called to keep me posted as the eye was overhead, long before I even thought to call him, and he didn’t seem “so mad” about doing it. (The Naples Daily News)
We had to be out of town for a week during this process due to an unplanned family medical emergency, and Catherine kept us posted and even emailed pictures when a change was needed and she wanted our approval. (The San Diego News)
At Hanhardt’s 2002 sentencing hearing, authorities also disclosed that in 1996 he asked another detective to keep him posted on a joint investigation with federal authorities on the importation of cocaine from South America. (The Chicago Tribune)