Radical reanalysis

Radical reanalysis is the reinterpretation of a linguistic unit as belonging to a new grammatical category not present in the respective grammar before.

A radical reanalysis is a special form of the more general concept of reanalysis, which is defined "as change in the structure of an expression or class of expressions that does not involve any immediate or intrinsic modification of its surface manifestation. Reanalysis may lead to changes at the surface level [...] but these surface changes can be viewed as the natural and expected result of functionally prior modifications in rules and underlying representations" (Langacker 1977: 58).

The same principles hold for a radical reanalysis, yet the changes on the underlying level are more drastic in so far as a new category is introduced to the grammar of the language.

Example
In sixteenth century English "a reanalysis of 'cunnan, magan, etc.', as a new category, 'modal' " took place (Lightfoot 1979:101). At this time a number of developments took place which formally distinguished this class of verbs from all other verbs. Among those developments were the development of the new infinitival construction with to for non-modal verbs, the loss of the subject-verb inversion construction for non-modal verbs, and the inability of modals to appear with the verb to have or in the past-participle form -en (also the past meaning of some of the forms, which were originally past tense, was lost) among other changes.

From those data Lightfoot concluded that "a radical re-analysis of pre-modals of the kind suggested here accounts naturally for the simultaneity of the seven changes taking place in the sixteenth century" (Lightfoot 1979:113).

Origin
The idea that "grammars can undergo radical re-structurings" was proposed by Lightfoot (1979: 81). He argued for this possibility on basis of his "paradigm case" of the English modals.

Other historical linguists remained skeptical towards the idea of radical reanalysis. Most preferred the idea of linguistic change as a gradual process rather than an abrupt switching of parameters (see McMahon 1994 for a summary of the criticism). Lightfoot's theory has been referred to as the "catastrophe theory of historical syntax" (McMahon 1994:116) in reference to his idea that a simple modification in the speakers' internal grammars can cause all the syntactic changes discussed for the case of English (pre-) modals.