In Trouble

Two common words that baffle even native English speakers are "inflammable" and "invaluable". So let's have a look at them.

The reason they're confusing, of course, is that "in-" is a very common prefix meaning "not": "invulnerable" means "not vulnerable", "insane" means "not sane", and so forth. And yet this clearly doesn't hold true for either of the words above: "invaluable" doesn't mean "not valuable", it means "enormously valuable", and "inflammable", confusingly and even dangerously, is an exact synonym for "flammable". So why doesn't "in-" work for these words?

As a little reflection will demonstrate, it doesn't work for quite a few other words, either. "Ingest", "inspire", and a whole host of other words aren't negated by "in-". The reason is that there are two drastically different prefixes that merely happen to look the same. One of them, from the Latin, does indeed mean "not": the other one means, logically enough, "in". "Inspire" is broken down into "in-" and the "-spire" that should be familiar from such words as "respire": it means "to breathe", and so "inspire" once meant "inhale" and now means, by way of a metaphor, "to breathe creative life into". "Ingest" is likewise "in-" plus the "-gest" that is familiar from "digest": it's from the Latin "genere", "to carry". (The "di-" in "digest", by the way, is from "dis-", "apart", as in "dissect", "to cut apart".) "In-" also shows up as "en-" ("enfold", "encapsulate") or "em-" ("embark", "emplace") sometimes; same root, different spelling, thanks to the tortuous history of the English language.

Did I say two? I lied. There's a third "in-", and it's a simple intensifier. It shows up in such words as "incantation" and, again in a different guise, "enfeeble" and "embolden". You can recognize this sense because it's often prefixed to a word that has more or less the same meaning on its own (though sometimes, as with "enfeeble", it has the effect of converting the original word to a different part of speech).

Now that I've thoroughly confused the issue, as is my way, let's get back to the two words in question. "Inflammable" isn't the result of attaching the negative prefix to "-flammable": it couldn't be, because it's the older word. "Inflammable" derives from "inflame"--that's the third sense of "in-", the one which intensifies and changes the part of speech--plus the standard verb-into-adjective suffix "-able", "able to be...." The word "flammable" exists only because of the obvious danger of a mistake arising from stencilling "inflammable" onto things that burn readily. Unfortunately, the misunderstanding is still with us.

"Invaluable", perversely, does have the first, negative sense of "in-", "not". The trouble is that it uses an older, literal sense of "valuable", one which is lost to us. If we cut "invaluable" into its three component parts, we can make some sense of it. "In-", "not": "value": and "able", "able to be". Something invaluable is something so precious that no value could possibly be assigned to it.