In this paper we discuss the issue of multiple versus unitary semantics. We argue that the notion of multiple semantics (as currently articulated) does not, in fact, represent a theory of semantic organisation but is, instead, an arbitrary conjunction of a set of independent assumptions which are either unmotivated or, if motivated, equally compatible with a unitary semantics hypothesis. Furthermore, the empirical evidence that has been cited as support for this hypothesis is equally compatible with variants of the unitary semantics hypothesis. A model of semantic processing—the Organised Unitary Content Hypothesis (O.U.C.H.)—that is able to account for reported patterns of dissociation of performance is discussed briefly.

We report the performance of a neurologically impaired patient, KE, whose frequent errors in reading, writing, naming, and comprehension were nearly always semantically related to the target response. To quantify this pattern, a large number of items were presented for tasks of verbal and written naming, oral reading, writing to dictation, word/picture matching, and naming from tactile exploration. Detailed analyses of his performance on these tasks show very similar rates and types of errors, regardless of the modality of stimulus or response. KE's homogeneous pattern of semantic errors across modalities is interpreted as evidence for selective damage to a semantic system common to all lexical processes. In addition, although KE demonstrated some spared knowledge of all items in response to picture stimuli, we were able to interpret all aspects of his performance without resorting to a proposal that there are modality-specific semantic systems. Finally, we show that our interpretation, which assumes a unitary, modality-independent semantic system, can also account for previously reported cases in the cognitive neuropsychology literature that have been taken as evidence for modality-specific semantic systems.

We describe the patterns of omissions (and substitutions) of freestanding grammatical morphemes and the patterns of substitutions of bound grammatical morphemes in 20 so-called agrammatic patients. Extreme variation was observed in the patterns of omissions and substitutions of grammatical morphemes, both in terms of the distribution of errors for different grammatical morphemes as well as in terms of the distribution of omissions versus substitutions. Results are discussed in the context of current debates concerning the possibility of a theoretically motivated distinction between the clinical categories of agrammatism and paragrammatism and, more generally, concerning the theoretical usefulness of any clinical category. The conclusion is reached that the observed heterogeneity in the production of grammatical morphemes among putatively agrammatic patients renders the clinical category of agrammatism, and by extension all other clinical categories from the classical classification scheme (e.g., Broca's aphasia, Wernicke's aphasia, and so forth) to more recent classificatory attempts (e.g., surface dyslexia, deep dysgraphia, and so forth), theoretically useless.