Some words can change in meaning so subtly that we don't even notice.
And to show you what I mean, I'm going to tell you a story.
A few years ago, I was at a wedding of a dear colleague of mine, and there were a few other linguists there.
They put us all at one end of one table, so that we wouldn't bother the other guests,
and so of course, we started talking about language.
And one person who is a lexicographer who is an editor of dictionaries said,
"Alright, I'm going to give you a sentence and I want you to tell me if you hear anything odd about this sentence."
So we all get ready for this sentence. And it was a sentence something like this:
"Mary and her partner had just moved in upstairs from us, and their boxes lay on the kitchen floor still unpacked."
We all listened to this. We listened to it again.
And some people were trying to figure out if there was
something wrong with lay/lie, but that's the red herring in the sentence.
But in the end, we all said, "sounds fine!"
Now, I don't know if you all thought it sounded fine or not, but the question I will ask you is,
Was there stuff still in the boxes, or not?
Now, in my head, the stuff is still in the boxes. But if we think about the sentence, the boxes were "still unpacked."
Which should mean that the stuff was out of the boxes. So in this sentence, "unpacked" means "packed."
Or it means "un-unpacked."
Some people will say, "This is impossible. A word cannot mean its opposite."
Well, it's not impossible. And, in fact, we have instances in English of other words that mean their opposite.
We don't have a lot of them, but we do have them.
If you think about the word "dust," dust can mean "to take the dust off of something,"
or "to put the dust onto something" as in you dust a cake with sugar.
"Sanction" is ambiguous because it can mean "to give permission to do something,"
or it can mean "to penalize for doing something."
"Cleave," which can mean "to cling to" or "to split apart."
Now, for each one of those words, there is a different story for how the word has come to mean its opposite.
But we do, as speakers, seem to be able to use context for at least some words, to be able to figure it out.
Now, I don't know what will happen with "unpacked" and whether
it will continue to mean "un-unpacked" for generations to come.
But I do know that it's not impossible for "unpacked" to mean both "unpacked" and "packed."
And I will forever be confused by what "bimonthly" means,
as to whether I'm going to the meeting twice a month,
or every other month, and I will always have to ask.