Back when Doug was in preschool, we took him to the doctor one day for a rash on his face and chest. The diagnosis: fifth disease. Fifth disease? What the hell was that? After Googling it, I learned that another name was slapped cheek syndrome, which made more sense. I didn’t object so much to a disease being called fifth disease, except that that was the only disease I’d come across with a numeric designation. Why hadn’t I ever heard of the first four diseases, or the diseases from the sixth onward?
As it turns out, diseases 1-4 go by the names measles, rubella, scarlet fever, and Duke’s disease, while the sixth is more commonly known as roseola. Furthermore, these numbers don’t encompass all diseases; just childhood diseases that involve rashes. That’s a little better, I guess, but why is it only the childhood rash diseases that got named this way? It reminded me of comics in the newspaper that do occasional running-gag strips on a theme like “Signs You’re the Parent of a Teenager” or “Essential Activities of Summer”, and each strip is labeled with a number. They don’t start with one and go sequentially; they label each entry with a randomly chosen number, as if to say, “The list goes on and on.” Ads in glossy magazines do this, too.
With that in mind, here is the topic suggestion from a reader named Karl, the second winner of my Grammar Girl book giveaway:
I’ve … noticed that 80% or more of Americans don’t use the past perfect form of verbs when the other clause in the sentence is a third conditional. They use the simple past form instead. I find myself doing it when I speak fast. For example, talking about a party which has finished: “If I knew you were there, I would have said hello” instead of using “had known”. Do other English speakers in other countries do the same thing?
“Third conditional”? This kind of conditional sentence is what I think of as a past-time counterfactual. Actually, I’m now moving to the terminology of the Cambridge Grammar of the English Language, and will refer to these as past-time remote conditionals. Remote refers to the falseness, or at least unlikelihood, of the situation described in the if clause. “If I had known you were there” — but I didn’t know. Anyway, this is the second or third time a commenter has used the term third conditional on me, so now I was finally curious enough to try to find out where this term came from, and what first and second conditionals might be. I still don’t know where it came from; the earliest I’ve found in Google Books is in an 1822 grammar of Spanish.
However, I can now tell you that a first conditional is a present- or future-time open conditional. For example, If you’re happy and you know it, clap your hands, or If you touch my stuff, I’ll kill you. It’s an open question whether you are knowingly happy, or whether you’ll touch my stuff. Maybe you are, or will; maybe you aren’t, or won’t.
A second conditional is a present- or future-time remote conditional, such as If you really loved me, you’d do it, or If I won the lottery, I’d quit my job. The implication is that you don’t really love me, and winning the lottery is unlikely.
The third conditional, of course, is the past-time remote conditional. I got all this from an online grammar reference from Capital Community College of Hartford, Connecticut. Now that I know about first, second, and third conditionals, though, not only do I still think the names are poorly chosen and uninformative, but they also miss a fourth possibility: past-time open conditionals. I’ve laid them all out in the table below, and you can verify that the bottom left corner is the one that got left out in the cold. It’s the Rodney Dangerfield of conditionals. Not because it has bulging eyes, starred in movies such as Back to School and Caddyshack, and does standup comedy with lots of one-liners, but because it gets no respect. But you probably figured that out.

Open and Remote Conditionals
What’s interesting about present-time remote conditionals and past-time open conditionals (the light green squares) is that they both use a past tense verb form: If he was/were sorry in the examples. CGEL looks at it this way: The past tense has several functions in English, only one of which is to express past time. Another function is to express “modal remoteness”–i.e. unlikely possibilities or impossibilities. Each of those functions is shown in a light green square. (For every verb except one, the verb form in these two squares would be identical. I’ve chosen the one and only verb for which there’s a difference: be, with its was for the open conditional, and were for the remote one. And even that distinction has disappeared for many speakers, who uniformly use was in sentences like these.) When both functions are in play, then a “double past tense” does the job. I show this with the darker shade of green in the bottom right, with the if clause in the past perfect tense: If he had been sorry.
I’ve noticed what Karl is asking about in past-time remote conditionals, too; for example, there was If only we swam as good as we look. Then there’s the old song “If I Knew You Were Coming, I’d've Baked a Cake”, which I first heard sung by Cookie Monster on Sesame Street. But how prevalent are these nonstandard conditionals, really? It’s hard to search for any and all conditionals that use a simple past tense or a past perfect tense, so instead I decided to search just for If I knew and If I had known in the Corpus of Contemporary American English (COCA), which contains 425 million words from 1990 to 2011. The search turned up 198 tokens of If I had known, 196 of which are past-time remote conditionals, like this one:
This was not a publicity stunt. Of course, if I had known that all of this would happen, I would have done this years ago!
(The other two were indirect questions, in which the if can be replaced by whether, as in, “He asked if/whether I had known about the cozy relationship between News of the World and Scotland Yard.” That’s not an actual example, but I forgot to record the ones I found.)
COCA produced 609 tokens of If I knew. Of these, 48 are present-time remote conditionals; for example:
I’ll say anything on a runway. I’d speak Hebrew or Arabic or Swahili if I knew them, anything to hedge my bets. But today I am too exhausted to bargain with God.
Sixteen of them are past-time open conditionals. Look, here’s one now:
Ethan was just a friend. … And if I knew what was good for me, I’d keep it that way. (past-time open conditional)
Twenty-two were irrelevant. The remaining nineteen are all nonstandard past-time remote conditionals, along the lines of:
We all know Julianne Moore is an Oscar-nominated, Emmy award-winning actress, but who knew that she liked to clean? If I knew that, I’d have given her Tuesdays at my house for a little light dusting.
Extrapolating that last number to the 609 hits for “if I knew”, I estimate that there are 120 nonstandard past-time remote conditionals. Add to that the nearly 200 standard past-time remote conditionals in COCA, we have a total of about 320 past-time remote conditionals. Of them, about 38% use the simple past tense instead of the past perfect. Well short of Karl’s guess of 80%, but still pretty sizeable. And of course, the numbers for what he hears and reads may well be nearer to 80%. Also, when I narrowed the search to If I knew then and If I had known then, I get a total of 37, only eight of which use the standard past perfect tense. In other words, 78% of the tokens used the simple past, right in line with Karl’s guess. I wonder if the signaling of past time by then makes it less necessary for the verb to do so.
To get an idea whether Americans or British used the nonstandard phrasing more, I looked at the British National Corpus (BNC), which contains 100 million words from 1985 through 1993. For If I knew, I got 90 hits, only two of which were nonstandard:
I would never have given him the sweet if I knew there was acid in it.
if I knew what I know now, I would never have left Pontypool.
For if I had known, I got 18 hits. That makes two nonstandard conditionals out of 20, for 10%. So, to the extent that the older BNC data still reflects modern usage, and to the extent that my single example is representative of past-time remote conditionals more generally, Americans are almost four times as likely to use a simple past tense in them as British speakers.
Feel free to run your own searches in COCA, BNC, or other corpora (maybe the Corpus of Historical American English) with other verbs. Let us know what you find. Karl, thanks for your suggestion!