A few months ago Braden asked in a comment about the history of what as a relative pronoun. (For my previous posts on relative pronouns, see here.) The history of relative pronouns in English is rather complicated, and the system as a whole is still in flux, partly because modern English essentially has two overlapping systems of relativization.
In Old English, there were a few different ways to create a relative pronoun, as this site explains. One way was to use the indeclinable particle þe, another was to use a form of the demonstrative pronoun (roughly equivalent to modern English that/those), and another was to use a demonstrative or personal pronoun followed by þe. Our modern relative that grew out of the use of demonstrative pronouns, though unlike the Old English demonstratives, that does not decline for gender, number, and case.
In the late Old English and Middle English periods, writers and speakers began to use interrogative pronouns as relative pronouns by analogy with French and Latin. It first appeared in texts that were translations from Latin around 1000 AD, but within a couple of centuries it had apparently been naturalized. Other interrogatives became pressed into service as relatives during this time, including who, which, where, when, why, and how. All of these are still in common use in Standard English except for what.
It’s important to note that what is still used as a nominal relative, which means that it does not modify another noun phrase but stands in for a noun phrase and a relative simultaneously, as in We fear what we don’t understand. This could be rephrased as We fear that which we don’t understand or We fear the things that we don’t understand, revealing the nominal and the relative.
But while all the other interrogatives have continued as relatives in Standard English, what as a simple relative pronoun is nonstandard today. Simple relative what is found in the works of Shakespeare and the King James Bible, but at some point in the last three or four centuries it fell out of use in the standard dialect. Unfortunately, I’m not really sure when this happened; the Oxford English Dictionary has citations up through 1740 and then one from 1920 that appears to be dialogue from a novel. Merriam-Webster’s Dictionary of English Usage says that in the US, it’s mainly found in rural areas in the Midland and South. As I told Braden in a response to his comment, I’ve heard it used myself. A couple of months ago I heard a man in church pray for “our leaders what guides and directs us”—not just a beautiful example of relative what, but also an interesting example of nonstandard verb agreement.
As for why simple relative what died out in Standard English, I really have no idea. Jonathan Hope noted that it’s rather unusual of Standard English to allow other interrogatives as relatives but not this one. In some ways, relative what would make more sense than relative which, since what is historically part of the same paradigm as who; what comes from the neuter form of the interrogative or indefinite pronoun in Old English, while who comes from the combined masculine/feminine form, as shown here. And as I said in this post, whose was originally the genitive form for both who and what, so allowing simple relative what would make for a rather tidy paradigm.
Perhaps that’s the problem. Hope and other have argued that standardized languages—or perhaps speakers of standardized languages—tend to resist tidy paradigms. Irregularities creep in and are preserved, and they can be surprisingly resistant to change. Maybe someone reading this has a fuller explanation of just how this particular little wrinkle came to be.
-  Jonathan Hope, “Rats, Bats, Sparrows and Dogs: Biology, Linguistics and the Nature of Standard English,” in The Development of Standard English, 1300–1800, ed. Laura Wright (Cambridge: University of Cambridge Press, 2000). ↩