Formulaic frames are patterns such as "I don't know", or "Can I have ..." which a child learns as a complete phrase, a formula. The claim is that these formulas can't be used by the child to produce new language. The child can't infer anything about the usage of modal verbs and main verbs from "Can I have ..."
In this same way, you might know that "Sono molto contento di conoscerla' means something like "Pleased to meet you" in Italian. But you can't infer anything about the structure of Italian, or produce new phrases from that.
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