Context 
For instance, it confuses the issue when we try to distinguish frontal from posterior syndromes by stating that only posterior cases show selection difficulties; the frontal patient does also. I have seen many posterior cases where there are addition, deletion, and linear types of phonemic paraphasia. It is not diagnostic of any group to show that substitution errors, for example, are more frequent than other error types. Buckingham and Kertesz (1976, p. 52) showed that, of the analyzable phonemic paraphasias of a neologistic jargonaphasic, there were far more substitution errors. Earlier, Blumstein (1973, pp. 4647) demonstrated that (using her classification of aphasia), when one analyzes the phonemic errors of Broca’s conduction, and Wernicke’s aphasics in terms of substitution, simplification, linear switch (“environment” in Blumstein’s terms), and addition, one finds that all the groups have the same relative difficulty. Each group had more substitution errors, followed by simplifications (deletions), and next by linear switches.
