According to etymonline.com, the word plain (as used in e.g. explain or plain English) first appeared in the sense of "flat, smooth, even". Later, the sense of "explicit, clear, evident" appeared.

I wonder,
what is the metaphor involving flatness that points towards "explicit, clear, evident"?


Other words that refer to "explicit, clear, evident" have underlying metaphors that are known from texts since ancient times:

  • lucid: dark room (non-seeing) is lightened up by a candle (seeing).
  • clear: the sky goes from cloudy (confusion) to clear.

Are there also old texts which use plain ("flat, smooth") as a metaphor for "explicit, clear, evident"? Where does this transferred sense come from?

Some guesses (without attested texts):

  • A turbulent sea surface as opposed to a still and smooth one? A metaphor for the mind.
  • A bumpy landscape as opposed to a flat surface? A metaphor for ease, uniformity, and simplicity of moving ahead.

Also, some possibly related words: explicit (unfold) and unpack.

  • 3
    The link (which you don't mention and I can't supply) between plain and unadorned seems apt.
    – Jim Mack
    Jul 28, 2022 at 13:57
  • @JimMack I appreciate the link. That hypothesis resonates with me. The unadorned is the essence of something, the core. So when we "explain", we point out the essence without the embellishments that might otherwise appear.
    – Michael
    Jul 28, 2022 at 14:23
  • 2
    If you look in the OED you'll find a lot of suggestive material with many different senses of the word in Middle English, but no definite statement to answer the question. The fact that all these senses (flat; unadorned; evident) seem to be 14th C or earlier, the comparative lack of texts from that era, and the lack of statements of authorial intent from that time ("I'm creating a metaphor vs I'm using an existing sense of the word") all mean a conclusive answer is unlikely to exist.
    – Stuart F
    Jul 28, 2022 at 14:33
  • 1
    I'd label the broader use of plain as a direct extension of the word, over any metaphorical use. After all, on day two of a company, "Quality Widgets" becomes a name with no implications of quality. Time can remove the imagery of a metaphor, if there was one. Jul 28, 2022 at 14:37

1 Answer 1


The English word plain is borrowed from Latin, which had it from two Proto-Indo-European roots, both with the shape *pelə-.

  • One meant To fill; with derivatives referring to abundance and multitude.

  • The other meant Flat; to spread.

Both are implicated in the meanings of English plain. The link in the metaphor is the fact that this is a Visual metaphor. What we notice about the world is that bodies of water have flat surfaces, which expand when they are filled or overfilled.

Much the same is true of anything that can flow, and geographical plains are flat (another word that comes from the same PIE root), and look like they've been filled up, like the sea. Indeed "sea of grass" is a common metaphor for plains and steppes. PIE was formed on the steppes of Central Asia over several thousand years of wandering.

On a plain, or steppe, one can see to a distant horizon, and everything in between. It's impossible to hide, and everything is clear as far as the human eye can see. That's where the "explicit, clear" sense comes from. To see more, you just get closer, like a microscope or a telescope; it's not hidden, it's not dark, it's there and one can see it.

Really, that's all you need. 3000 years of visual experience will have a tendency to stick in the mind when the experiencers go on to other things. It's as plain (the saying goes) as the nose on your face, a piece of our optical view that we see whether we want to or not, and consequently rarely notice.

  • 1
    I feel very grateful for this answer, John. I can picture standing on a steppe and seeing the distant horizon. This resonates, makes sense, and integrates wonderfully within me. Thank you.
    – Michael
    Jul 28, 2022 at 16:13
  • 1
    Great answer. Upvoted. In fact, the earliest sense of plain is a flat terrain which is still used today. Additionally, per OED, plain was used in geometry and other areas also for a flat surface but it is superseded by plane.
    – ermanen
    Jul 28, 2022 at 22:58
  • Plain and plane are the same word, just spelled differently for different contexts. Spelling is irrelevant, especially in a world of bad spellers. Aug 2, 2022 at 13:43

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