Given a generalized Phrase-marker, we construct a transformational derivation by applying the sequence of transformational rules sequentially, "from the bottom up" - that is, applying the sequence of rules to a given configuration only if we have already applied it to all base Phrase-markers embedded in this configuration. If none of the transformations blocks, we derive in this way a well-formed surface structure.
- Chomsky (1969), Pag. 143