I hate when someone starts a monologue by needlessly invoking a dictionary definition for some word. Few openings can ruin a graduation speech faster than “Webster’s defines ‘scholarship’ as …”. (Even the Yahoo! Answers community knows this.) For most common words, the dictionary definition is just a simplified, neutered form of the rich definition that native speakers have in their heads. There’s no need to tell me less about a word than I already know.
Unfortunately, I simply can’t come up with another way to start today’s post. I recently ran across this analysis of can’t help but, an idiom that (if you can believe it) the author finds illogical:
“Try to avoid the can’t help but construction. While it has been around for a while, most grammarians agree that it’s not the most logical construction. It’s considered to be a confused mix of the expressions can but and can’t help.”
Before we try to “logically” analyze idioms, let’s reflect for a moment what an idiom is. Here it comes — The Oxford English Dictionary defines an idiom (in its third noun sense) as:
“A form of expression, grammatical construction, phrase, etc., used in a distinctive way in a particular language, dialect, or language variety; spec. a group of words established by usage as having a meaning not deducible from the meanings of the individual words.”
I’ve bolded that last bit because that’s the key point: an idiom is an idiom when its meaning is well-known among users of the language but does not come from strict interpretations of the words themselves. If you say someone has idiomatically kicked the bucket, there’s no bucket, there’s no kicking motion, and it actually means they died. Logical analysis of kick the bucket won’t get you anywhere near the actual meaning.
With that in mind, let’s look at can’t help but. Surely, most fluent English speakers — including those who disparage it as “illogical” — know what it means. If that meaning can be deduced from the words and syntax of the construction, then hooray, it’s fine, because it’s grammatical. If that meaning cannot be deduced from the words and syntax of the construction, then hooray, it’s still fine, because it fits exactly the definition of an idiom. It doesn’t matter if the meaning is deducible or “logical”, whatever that means. (For some thoughts on why I put “logical” in quotation marks when talking of grammatical logic, see Emily Morgan’s post on the logic of language.)
You might think that I’ve done some rhetorical sleight-of-hand in the last paragraph by saying that can’t help but either makes sense or is an idiom. What if it isn’t an idiom, but just an illogical corruption of can help but? I’ve got two thoughts on that.
The first is a simple matter of history. The OED records the use of can’t help but starting in 1894, but I’m finding it in Google Books further back than that. Here are examples from 1852 [Uncle Tom's Cabin], 1834, and 1823. Similar investigation antedates can help but around the same time, 1842 and 1834. There’s no clear evidence that one form predates the other, so there’s no evidence that cannot help but is a corruption of the correct form.
The second point is that the supposedly logical alternatives can help but and can’t help make no more sense than cannot help but. I don’t understand the above claim that can’t help but is “not the most logical construction”. Maybe it isn’t; I’ll grant that it’s not as immediately interpretable as “I am walking” or something. But if can’t help but isn’t logical, why are the alternatives can help but and can’t help logical? What meaning is there for help that makes can’t help eating the cake mean “can’t stop myself from eating”? Whatever it is, it’s strictly idiomatic; you couldn’t, for example, write “I am helping eat the cake” with the meaning “I’m stopping myself from eating the cake”. In fact, it means exactly the opposite!*
For confirmation, I checked in the OED, and this meaning occurs only in these idioms. So can help but and can’t help aren’t “logical” either; they’re the result of people applying idiomatic knowledge to the interpretation of the construction. As soon as you expect help to mean something other than its standard aid-related usages, you’re going idiomatic, and logic pretty much goes out the window.
This is a long way of arguing that can help but and can’t help but are both grammatically reasonable. Shouldn’t we decide on one form over the other? Well, no. I know that prescriptivists love doing that, but it’s not the way language really works. The fact of the matter is that both are common, and in the opinion of the Merriam-Webster Dictionary of English Usage, both are standard.
But if that still won’t placate you, if you simply must be told which one is better, the perhaps surprising answer is that it’s the “illogical” can’t help but. The Corpus of Historical American English has 243 examples of can not help but to a mere 6 of can help but, and Google N-grams shows cannot help but dominating since 1840. (And personally, can help but doesn’t exist in my idiolect.) If you want to write the more common form, go with can’t help but. If can help but seems better to you, go with that.
Summary: Can’t help but is a perfectly standard idiom, meaning “can’t stop myself from”. It’s also the more common choice, historically and contemporarily, over can help but, even though both options are grammatical and standard in English. (Can’t help Xing is fine too, of course.)
*: Furthermore, doesn’t can’t help Xing have the potential to be even more confusing than can’t help but? If I say “I can’t help putting together your bike today”, am I saying that I can’t do it or I can’t stop myself from doing it?