rule, plays an especially important role in what is to come here. Two simple cases are the principles stated
informally as (17a, b). They can best be understood in the context of section 1.6, which discussed how
corresponding constituents in the phonological, syntactic, and semantic structures in Fig. 1.1 are linked by
subscripts.(17) a.If the semantic structure of a sentence contains an Agent (the entity bringing an action about), it (normally)
corresponds to the subject in syntactic structure.
b. The linear order of elements in phonological structure (normally) corresponds to the linear order of
corresponding elements in syntactic structure.Suchprinciples appear ina widerangeoftheoriesofgrammar; wewilldiscuss theminChapter 5. Importantly, inmany
ofthese theories, relationssuch as theactive-passivealternationare notcaptured in terms of derivational rules. Rather,
the grammar contains alternative interface rules relating syntactic structure and meaning, such that active and passive
syntactic structures map into essentially the same meaning. We see here one of the major divides among theories of
grammar: should such semantic relations among sentences be captured by more elaborate derivational rules, or by
more elaborate interface rules? (Note how this relates to the alternative treatments of Tense in section 1.6.)
- A morecomplextypeofconstraint,whichmightbecalleda“meta-constraint,”appliesnotbetweentwolevels
of structure in the same derivation, but between two or more alternative derivations. A situation where this
seems unavoidable ismorphological blocking. For example, the standard procedure for producing the past tense
of an English verb is to add−d;^22 this applies to anythingthat counts as a verb, even new made-up verbs like
fax. However, thisproceduredoes notworkinthe180 orsocases whereitissupplanted byanirregular form;
thus we saywentandshookinsteadgoedandshaked. In other words, the derivation ofgo+−d, although in
principle legitimate, is blocked because there is another way to express the same combination of meanings.
This sort of phenomenon is ubiquitous in principles of morphology (word structure).
Meta-constraintswith a much moreglobal spiritappear in both theMinimalist Program and OptimalityTheory. Inthe
former, there are in principle many ways to get from an underlying form to an acceptable surface form, but one of
these is chosen in preference to the others in part by a meta-constraint called Economy. This constraint gives priority
to the shortest derivation that satisfies all the other constraints.
50 PSYCHOLOGICAL AND BIOLOGICAL FOUNDATIONS
(^22) In turn, -d is pronounced -t or -əd depending on thefinal consonant of the verb, along lines similar to those discussed in connection with the English noun plural in
section 1.3.