pairs (e.g. spring-sprung, sing-sang) may allow for memory-based generalization to new irregularities, either from real words (bring-brought) or from novel ones (spring-sprung). This ability to generalize could underlie some degree of productivity within the memory system. While declarative memory deals with irregularities of morphology, procedural memory uses regular phonology and regular morphology. Procedural memory system is used by grammar, where grammar is defined by the building of a rule governed structure. Language's ability to use grammar comes from procedural memory, making grammar like another procedure. It underlies the learning of new, and already learned, rule-based procedures that oversee the regularities of language, particularly those procedures related to combining items into complex structures that have precedence and hierarchical relations- precedence in the sense of left to right and hierarchical in the sense of top to bottom. Procedural memory builds rule-governed structure (merging or series) of forms and representations into complex structures such as: Phonology Inflectional and derivational morphology Compositional semantics (the meaning of composition of words into complex structures) Syntax Broca and Wernicke's Brain Region Broca's area is important to procedural memory, because, "Broca's area is involved in the expressive aspects of spoken and written language (production of sentences constrained by the rules of grammar and syntax)." Broca's area corresponds to parts of the inferior frontal gyrus, presumably Brodmann's area 44 and 45. Procedural memory is affected by Broca's aphasia. Agrammatism is apparent in Broca's aphasia patients, where a lack of fluency and omission of morphology and function words occur. While those with Broca's aphasia are still able to understand or comprehend speech, they have difficulty producing it. Speech production becomes more difficult when sentences are complex; for example, the passive voice is a grammatically complex structure that is harder for those with Broca's aphasia to comprehend. Wernicke's area is crucial for language development, focusing on the comprehension of speech, rather than speech production. Wernicke's aphasia affects declarative memory. Opposite of Broca's aphasia, paragrammatism is apparent, which causes normal or excessive fluency and use of inappropriate words (neologisms). Those with Wernicke's aphasia struggle to understand the meaning of words and may not recognize their mistakes in speech. History The study of human memory stretches back over the last 2000 years. An early attempt to understand memory can be found in Aristotle's major treatise, On the Soul, in which he compares the human mind to a blank slate. He theorized that all