We normally produce a speech sound for it to be transmitted and heard. An ideal description of speech sounds would thus include information concerning their production, transmission and reception (hearing). Correspondingly, speech can be described and classified in articulatory, acoustic and auditory terms. Such an analysis and description of speech sounds is the subject matter of Phonetics, commonly known as the study of speech sounds. Phonetics describes a sound in terms of the movements of the organs of speech, the physical properties of the sound produced and the features perceived by the listener. But such an exhaustive description is very complex and is beyond the scope of this book. Since our purpose is to teach the pronunciation of English, our analysis will be based mainly on the production of sounds (articulation of sounds) - i.e., articulatory phonetics - and partly on how they may be heard by the listener - i.e., auditory phonetics.
Speech sounds are classified and categorized into vowels and consonants. The sounds regarded as vowels are described in terms of their articulation and on the basis of auditory perception, while consonants are best described in terms of their articulation. Vowels and consonants are usually understood with reference to the alphabets of a language; for instance, the letters a, e, i, o, and u in English generally represent the vowel sounds of the language, and the rest of the alphabets usually represent the consonant sounds.