Why did the frequent frames in German child-directed speech gather such inconsistent sets of grammatical categories? Categories that often ended up in the same frame were noun, pronoun, main verb, auxiliary verb, and adverb. There are at least three explanations. First, this is due to the fact that virtually all definite articles that were registered as a left framing element were used both as a determiner and a pronoun. For instance, a frame like das_x_nicht categorized verbs as well as adverbs, nouns, and pronouns (e.g., das_ist_nicht (verb; is); das_noch_nicht (adverb; still); das_huhn_nicht (noun; chicken); das_beide_nicht (pronoun; both)). Das was used pronominally if followed by a verb or an adverb, but was used as a determiner if followed by a noun or a pronoun. Second, frames sometimes crossed the boundaries of intonation units within a sentence. Although frames were not allowed to cross utterance boundaries considering the whole sentence as one intonation unit, there were no restrictions for frames within one sentence; that is, speech pauses were ignored as boundaries of intonation units. For instance, the frame das_x_eine collected verbs most of the time but gathered adverbs as well. In the latter case the frame crossed a pause: “Was ist das_da,_eine?”(“What’s that, a?”). Third, for some frames, low accuracy scores together with high diversity scores might mirror the variability in the relative ordering of the subject and the verb in German. For instance, the frame ich_x_nicht categorized, among others, verbs (e.g., wissen“to know”) and adverbs (e.g., wirklich“really”). Both could occur at either side of the subject of the sentence, which is the right-framing element of the frame. Whenever there is an adverb or a pronoun in the slot position of this frame, the subject ich (I) must be preceded by a verb. In contrast, whenever there is a verb in the slot position, the subject ich (I) can be preceded by an adverb. The following sentences, which are basically the same speech act for the same event and contain the same lexical items, are possible: “wirklich, ich_weiß_nicht was du meinst” (Really, I don’t know what you mean), “Was du meinst weiß ich_wirklich_nicht” (What you mean know I really not). Whereas the last two explanations might apply to Dutch frequent frames as well, the first reflects a characteristic of German only.
Furthermore, Mintz (2003) hypothesized that in languages with a more flexible word order co-occurrence patterns at a different level of granularity, for example, at the level of sublexical morphemes, might be more informative. Following this, Erkelens (2009) found evidence for categorization from frequent morpheme frames for 16-month-old children learning Dutch. Evidence for productive morpheme frames in German comes from a corpus study showing young children’s sensitivity to the phonological patterns in word structure (word endings) and their co-occurrence with gender marked articles (Szagun, Stumper, Sondag, & Franik, 2007). Further, frequent morpheme frames in German seem to show higher accuracy scores as compared to frequent word frames (Höhle, personal communication).