Some, but not all, languages with fixed stress exhibit lexical exceptions to their stress rule. Under the assumption that lexical exceptions can occur in a language only if its native speakers can perceive stress contrasts, I argue that the presence of these exceptions depends on the age at which infants discover the stress rule of their language. If the stress regularity is easy to infer from the surface speech stream, then it will be acquired very early, and stress will not be encoded in the phonological representation of words in the mental lexicon; as a consequence, stress contrasts are not well perceived by adult speakers and lexical exceptions are excluded. If, by contrast, the regularity is difficult to infer, then it will be acquired relatively late, after the format of the phonological encoding of words has been fixed. That is, stress will be redundantly encoded in the mental lexicon, and lexical exceptions can thus be perceived and stored by adult speakers. A typological survey concerning the occurrence of exceptions in languages with fixed stress supports this proposal. A comparison with a metrical approach to exceptional stress is made, leading to a proposal about the division of labor between psycholinguistics and theoretical phonology.

A number of recent attempts by nonlinguists to reconstruct linguistic evolutionary trees have made news. Reconstructions of the phylogeny of the Indo-European (IE) family of languages are especially well represented; well-known examples include Rexová et al. 2003, Gray & Atkinson 2003—which is discussed by Searls (2003) and briefly reported in U.S. news & world report (10 December 2003)—and Forster & Toth 2003, which also generated considerable attention in the popular media. Scientific linguists have not been impressed for a variety of reasons. Though no two of the publications in question exhibit exactly the same weaknesses, all can be impugned on one or more of the following grounds: the linguistic data employed have not been adequately analyzed, or—in some cases—even competently analyzed; the model of language change employed has not been shown to fit the known facts of language change; attempts to fix the dates of prehistoric languages have ignored the fatal shortcomings of glottochronology discovered by Bergsland and Vogt (1962; see further §4); the researchers assume that vocabulary replacement is governed by a LEXICAL CLOCK (similar to the controversial MOLECULAR CLOCK posited by some biological cladists); and/or the data set used is too small to yield statistically reliable conclusions.

Many factors affect the ease or difficulty of understanding a word in a sentence, including the lexical frequency of the word, the syntactic context, the discourse context, the intonation of the sentence, and the plausibility of the situation described by the sentence thus far (see Gibson & Pearlmutter 1998 and Tanenhaus & Trueswell 1995 for summaries of relevant factors and evidence). In order to investigate any one of these factors, it is therefore necessary to control for the others. One factor that has recently begun to be investigated in the psycholinguistics literature is the derivational complexity of different lexical structures. In order to investigate lexical derivational complexity, researchers have compared reading times and sentence-acceptability judgments for different kinds of noun-verb pairs. Unfortunately, these measures are necessarily contaminated by potential differences in plausibility between the real-world situations described by the particular sentences that are used to instantiate the structures. For example, consider McKoon and Macfarland's (2000; henceforth M&M) evidence that externally caused change-of-state verbs are more complex than internally caused change-of-state verbs (see Levin & Rappaport Hovav 1995 for a lexical-semantic distinction between the two types of verbs). M&M demonstrated that participants were slower in deciding that externally caused sentences like la were acceptable than they were in deciding that internally caused sentences like 1b were acceptable.