This volume presents an in-depth study of the so-called irregular Past Tense (sing/sang) and Noun Plural (foot/feet) forms with Internal Vowel Alternation (IVA) in English demonstrating that they possess both a fixed phonological and semantic regularity. The innovative sign-oriented analysis and inductive methodology employed in this study are further supported by additional first language acquisition data, experimental studies and historical evidence. The data culled from multiple linguistic anthologies, dictionaries and thesauri have shown that although the IVA process comprises a relatively small number of nominal and verbal forms in Modern English, IVA, originally, was a prevalent and productive process in Old English, Indo-European and other language families. The results of this empirical study present and introduce a novel classification based on the regular and systematic iconic-phonological and semantic nature of all these diverse IVA processes both nominal and verbal that has been maintained throughout the history of English.