Here's a breakdown of how "flat" can manifest:
* Flat structures in languages with case systems: Languages like Latin, German, or Russian use case markings (nominative, accusative, dative, etc.) on nouns and pronouns to show their grammatical role in a sentence. A "flat" structure would be one where these case markings are missing or inconsistent, resulting in ambiguity about the grammatical roles of the words. For example, a sentence might lack case markings on pronouns, making it unclear who is the subject and who is the object.
* Flat structures in languages without case systems: Even in languages like English, which rely heavily on word order, a "flat" structure could be used to describe unusual sentence constructions that lack clear markers of grammatical function. This might involve unusual word order, missing prepositions, or the absence of other functional words that typically indicate grammatical roles. This would usually be considered stylistically marked or non-standard.
* Flat adverbs and adjectives: In some theoretical linguistics, the term "flat" can describe adverbs or adjectives that don't show typical inflectional changes (e.g., comparative or superlative forms) even though they might semantically modify another word.
* Flat serial verbs: In some languages with serial verb constructions, the verbs may lack the usual grammatical markers that typically indicate their functions (e.g., tense, aspect, mood) making them seem less differentiated structurally.
In essence, "flat" in grammar signals a lack of the usual morphological or syntactic distinctions used to establish grammatical relationships between words in a sentence. It often leads to ambiguity or a less clear grammatical structure than expected. The exact meaning of "flat" can depend on the linguistic framework being used.