Capping our sentences off with complementizer phrases is a nice, simple addition to our theory of how sentences get built — one which nonetheless manages to do a lot of work for us. But as basic as the idea might seem, there are lots of little eccentricities that end up coming along for the ride.
For one, all our examples involve actually pronouncing the complementizer, which heads the CP; this isn’t always necessary. In many cases, this word gets dropped altogether, without much effect (though, we might still suppose the structure is there, holding everything up).
(1a) Fred Johnson believed that the insurgents had refused to surrender
(1b) Fred Johnson believed the insurgents had refused to surrender
This is true with other kinds of embedded clauses, too, like relative clauses inside noun phrases.
(2a) the planet that Alex came from
(2b) the planet Alex came from
What’s kind of quirky about all this is that we aren’t always allowed to do it. In (2) above, the subject of the relative clause is “Alex,” so deleting “that” works out fine. But relative clauses can also come without subjects, and in those cases, things don’t run so smoothly. (3b) below works as a sentence, but not as a relative clause; you can’t embed it in something bigger, like “The people live on the station want to be treated fairly.” Sometimes, the complementizer has to show up for work.
(3a) the people that live on the station
(3b) *the people live on the station
And there are times, too, when it has to stay home. When the subject right after a complementizer moves — say, because the whole thing has been turned into a question — we get a sort of mirror image of the pattern we just saw.
(4a) You think that the detective found Julie
(4b) *Who do you think that found Julie?
Because we often think of words as leaving a trace of themselves behind after moving, this pattern has come to be known as the that-trace effect, where complementizers just can’t seem to stand being next to a newly vacant spot. Remarkably, this effect seems to be found in unrelated languages throughout the world.
(5) French: *Qui a-t-il dit que _ voulait voir Marie?
Who has he said that _ wanted to see Mary?
(6) Levantine Arabic: *ʔayy bint Fariid kaal innu _ ištarat l-fusṭaan?
Which girl did Fariid say that _ bought the dress?
The effect even seems to be at play with other complementizers (e.g., “for”), suggesting there might be a more general complementizer-trace effect.
(6a) Who would you prefer for Miller to meet _ at the station?
(6b) *Who would you prefer for _ to meet Diogo at the station?
Finally, there are some cases where we can get away with replacing the complementizer with a wh-word, like “who” or “when.” Setting aside more prescriptive attitudes against using “that” in place of “who” when talking about people, the sentences below are otherwise equally acceptable.
(7a) a passenger that the ship was carrying
(7b) a passenger who the ship was carrying
But this is a bit surprising, when you consider what the structures of CPs usually look like. Typically, we don’t consider wh-words and complementizers to be one and the same thing; instead, we tend to think they occupy a position inside the CP different from the complementizer, since ordinary questions see wh-words showing up high in the tree.
And since there seems to be plenty of room, you might think we could build a structure like (9), with both a wh-word and complementizer inside the relative clause.
However, there’s a strong prohibition against these kinds of structures, aptly titled the Doubly-Filled-Comp Filter (the DFCF). This prevents us from saying things like (10).
(10) *a passenger who that the ship was carrying
As of now, the exact reason that the DFCF exists is still an open question, especially given that English used to be able to accommodate both wh-words and complementizers at the same time.
(11) Old English: Eadig bið se man se ðe gemet wisdom
blessed is the man who that finds wisdom
But a little bit of mystery can be a good thing, if you’re the type who likes a puzzle. And it definitely goes to show you that answers often just bring more questions along with them!
So how about it? What do you all think? Let us know below, and we’ll be happy to talk with you about questions and embedding and how CPs work. There’s a lot of interesting stuff to say, and we want to hear what interests you!
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