Suppose that we have a lexical entry ('D', 'C') where 'D' is a phonological feature matrix and 'C' is a complex symbol containing the feature [+'X'—'Y']. We stipulated previously that the lexical rule permits 'D' to replace the symbol 'Q' of the preterminal string 'φQψ' provided that 'Q' is not distinct from 'C'. Suppose that we now require, in addition, that this occurrence of 'Q' actually appear in the frame 'X'—'Y'. That is, we require that 'φQψ' equal 'φ1φ2Qψ1ψ2', where φ2 is dominated by 'X' and ψ1 by 'Y' in the Phrase-marker of 'φQψ'. This convention can be formulated precisely in terms of the notion "Analyzability" on which the theory of transformation is based.
- Chomsky (1969), a pag.121