Every sound belongs to one or other of two main classes known as vowels and consonants. Vowels are classified by lack of obstruction to the air stream, defused muscular tension, and weak air stream. Consonant articulatory obstruction to the air steam, muscular tension concentrated in the place of obstruction, strong air stream. The particular quality of a consonants depend on the work of the vocal cords, the position of the soft palate and the kind of noise that results when the tongue or the lips obstruct the air passage. An articulatory obstruction may be complete (is formed when the organs of speech come in contact with each other and the air passage through the mouth is blocked) or incomplete (an articulatory organ is held close to a point of articulation without blocking the air passage)