Reanalysis is a language-change mechanism in which speakers reinterpret grammatical structure without surface form change. For example, 'a napron' was reanalyzed as 'an apron' (morpheme boundary rebracketing). Reanalysis typically occurs when ambiguity allows alternative parsings; comprehenders choose a different analysis, and over generations, the reanalyzed structure becomes standard, driving systematic grammatical change through individual reinterpretation.
From your study of language variation and change, you know that languages change over time through gradual, systematic processes — sound shifts, semantic drift, morphological erosion. Reanalysis adds a different mechanism to this picture: not gradual phonetic drift, but a structural *reinterpretation* that can occur without any audible change in surface form. The words stay the same; the grammar changes.
The classic morphological examples illustrate the basic mechanism. Middle English speakers said "a napron" (from Old French *naperon*, meaning a small tablecloth). The string "a napron" is phonetically ambiguous: the morpheme boundary could fall as "a + napron" or "an + apron." Both parsings produce identical speech. But at some point, enough speakers chose the second parsing that "an apron" became the standard — and the word "napron" disappeared entirely. Similar rebracketing drove the creation of "a newt" (from "an ewt"), "a nickname" (from "an eke-name"), and "an adder" (from "a nadder"). The article was incorporated into the noun, or vice versa, through nothing more than a shift in how listeners parsed what they heard.
More consequential reanalyses operate at the syntactic level. English modal verbs (*can*, *will*, *shall*, *may*) were once ordinary full verbs: they could take direct objects, appeared in all tenses, and allowed infinitive complements like other verbs. Over centuries, their distribution narrowed. They lost productive past-tense forms (we say "could" as a suppletive form, not an inflected past of "can"), stopped taking direct objects, and came to occupy a distinct grammatical position. At some stage, speakers reanalyzed them not as main verbs but as a distinct class of grammatical auxiliaries. This is grammaticalization: a lexical item with full content meaning is reanalyzed as a grammatical element. The process typically chains: a content word becomes an auxiliary, an auxiliary becomes a clitic, a clitic becomes an inflectional ending, the ending erodes. Each step is a reanalysis.
The critical enabling condition for reanalysis is structural ambiguity: when a sequence of words or morphemes admits two parsings, the door is open for reinterpretation. Comprehenders build the structural analysis that fits most naturally with their existing grammar; when enough speakers converge on the same alternative analysis, the reanalysis propagates through the speech community and eventually becomes the new standard. From your study of movement and transformations, you can see why structural reanalyses matter: changing what grammatical category a form belongs to, or where a morpheme boundary falls, cascades through the grammar — affecting what syntactic positions are available, what agreement patterns apply, and what further changes become possible. Reanalysis is not random drift; it is the mechanism by which ambiguity in parsing translates into systematic grammatical change across generations.