<P> It has been frequently claimed that there is a contrast involving tone between wh - questions and yes / no questions, the former being said to have falling tone (e.g. "Where did you \ PUT it?") and the latter a rising tone (e.g. "Are you going / OUT?"), though studies of spontaneous speech have shown frequent exceptions to this rule . "Tag questions" asking for information are said to carry rising tones (e.g. "They are coming on Tuesday, / AREN 'T they?") while those asking for confirmation have falling tone (e.g. "Your name's John, \ ISN 'T it ."). </P> <P> The pronunciation system of English has undergone many changes throughout the history of the language, from the phonological system of Old English, to that of Middle English, through to that of the present day . Variation between dialects has always been significant . Former pronunciations of many words are reflected in their spellings, as English orthography has generally not kept pace with phonological changes since the Middle English period . </P> <P> The English consonant system has been relatively stable over time, although a number of significant changes have occurred . Examples include the loss (in most dialects) of the (ç) and (x) sounds still reflected by the ⟨ gh ⟩ in words like night and taught, and the splitting of voiced and voiceless allophones of fricatives into separate phonemes (such as the two different phonemes represented by ⟨ th ⟩). There have also been many changes in consonant clusters, mostly reductions, for instance those that produced the usual modern pronunciations of such letter combinations as ⟨ wr - ⟩, ⟨ kn - ⟩ and ⟨ wh - ⟩ . </P> <P> The development of vowels has been much more complex . One of the most notable series of changes is that known as the Great Vowel Shift, which began around the late 14th century . Here the (iː) and (uː) in words like price and mouth became diphthongized, and other long vowels became higher: (eː) became (iː) (as in meet), (aː) became (eː) and later (eɪ) (as in name), (oː) became (uː) (as in goose), and (ɔː) became (oː) and later (oʊ) (in RP now (əʊ); as in bone). These shifts are responsible for the modern pronunciations of many written vowel combinations, including those involving a silent final ⟨ e ⟩ . </P>

What is the implication of the number of english vowels and its vowel sounds to speaking