The sound variations in words, their derivatives and grammatical form words, are known as sound alternations. For example: the dark [l] in spell alternate with the clear [l] in spelling; combine (n) [‘kσmbain], combine [kəm’bain] where [n] in the stressed syllable of the noun alternates with the neutral sound. It is perfectly obvious that sound alternations of this type are caused by assimilation, accommodation and reduction in speech. To approach the matter from the phonological viewpoint, it is important to differentiate phonemic and allophone alternations. Some sound alternations are traced to the phonemic changes in earlier periods of the language development and are known as historical. Historical alternations mark both vowels and consonants, though the alternating sounds are not affected by the phonemic position or context. The sounds changes, which occurred in the process of historical development of the language, are reflected in present-day English as alternations of phonemes differentiating words, their derivatives and grammatical forms. The following list of examples presents the types of alternations:
1. Vowel alternations.
1.1 Distinction of irregular verbal forms [i:-e-e] mean - meant - meant; [i-æ-A] sing - sang - sung; [i-ei-i] give - gave - given;
1.2 Distinction of causal verbal forms: [i-e] sit - set; [ai-ei] rise - raise; [o - e] fall-fell
1.3 Distinction of parts of speech in etymologically correlated words [a: - æ] class - classify, [o: - e] long - length; [ei - æ] nation - national
2. Consonants alternations
2.1 Distinction of irregular verbal forms [d - t] send - sent
2.2 distinction of parts of speech [s - z] advice - advise; [k - t∫] speak - speech;
3. Vowel and consonant alternations [i - ai] + [v - f] live - life; [a: - ae] + [θ - ð] bath - bathe.