It must be opposite day, or opposite century. At some point in the not-very-distant past, Americans started to say “off” when they meant “on,” and Dr. Boli does not know why they began or how to make them stop.

An example: “Weevil’s study builds off the work of the scholar Sir Martinet Weedwhacker.” (Names have been changed to protect the innocent, but otherwise this is a direct quotation.)

Here is an example from the New York Times as quoted by Merriam Webster:

Diets at the time, for rich and poor alike, were based off the humoral science of the ancient Greeks…

Now, a base is a foundation, a thing to be built on. Clearly if you build off the foundation, it means that you are building somewhere else. If Weevil is building off Weedwhacker’s work, that would mean that his work has nothing to do with Weedwhacker’s. If something is based off the humoral science of the ancient Greeks, it has nothing to do with that humoral science. It is based on something else.

But obviously that is not what these writers mean. They say “based off” when they mean “based on.” They say “built off” when they mean “built on.”

Dr. Boli would not hire any of these people as architects.

It seems to Dr. Boli that many of these peculiar errors in English—and he has no qualms about calling “off” for “on” an error—spread through the pedantic instinct. In the beginning, they are picked up precisely because they are rare. Everybody says “based on”; we hear an authority figure say “based off,” and we assume that, because it is not what everybody says, it must be a more correct alternative to what everybody says. These innovations thus take root most firmly among the middlebrow population who have some college education and a desire to be correct in English, but do not feel very confident of their own understanding of what “correct” would mean. The little snowball rolls down the hill and becomes an avalanche, and pretty soon your average middlebrow will hear somebody say “based on” and smugly correct him: “You mean based off, don’t you?”

This particular example is also part of what may be a more disturbing trend in American English, which is the tendency to use a word or phrase to mean its opposite. More and more Dr. Boli runs across people who consistently write “would” or “could” when they mean “wouldn’t” or “couldn’t,” and if that ever becomes standard usage, verbal communication will be at an end, and we will be reduced to the level of grunting and whining animals.

There may be no way to stop “based off,” “built off,” and the like from becoming standard English. But that will mean that the architectural metaphor is completely lost, and thus those phrases will be fairly good indicators that the speaker is merely babbling and not saying anything worth listening to.