I’ve been enjoying Steven Pinker’s Words and Rules: The Ingredients of Language (1999). More technical and focused than his popular bestseller The Language Instinct, it is effectively a monograph on linguistic irregularity, examining in particular how we inflect verbs for past tense and plurality, and what the exceptions can tell us about the structure of language and our minds.
In chapter 7, ‘Kids Say the Darnedest Things’, Pinker points out that children sometimes know that the mistakes they make are mistakes. He cites Dan Slobin and Tom Bever, psycholinguists who inserted their children’s speech errors into their own speech and recorded the results:
TOM: Where’s Mommy?
CHILD: Mommy goed to the store.
TOM: Mommy goed to the store?
CHILD: NO! (annoyed) Daddy, I say it that way, not you.
CHILD: You readed some of it too . . . she readed all the rest.
DAN: She read the whole thing to you, huh?
CHILD: Nu-uh, you read some.
DAN: Oh, that’s right, yeah, I readed the beginning of it.
CHILD: Readed? (annoyed surprise) Read! (pronounced rĕd)
DAN: Oh yeah, read.
CHILD: Will you stop that, Papa?
Pinker infers from this, and from the evidence of more controlled studies, that children know irregular forms better than we might suppose; as they progressively master these forms, their errors are “slip-ups in which they cannot slot an irregular form into a sentence in real time”. Adults make similar slips, though nowhere near as often.