it may aid writers in spelling, but mislead readers in pronunciation. The rest are empty letters, which never have a sound, e.g., in honor, in answer, in Sarah, in island, in subtle. These may present the greatest difficulty to writers and often to readers, as well. The distinction between "endocentric" digraphs and empty letters is somewhat arbitrary. For example, in such words as little and bottle, one might view as an "endocentric" digraph for , or view as an empty letter; similarly, with or in buy and build. Not all silent letters are completely redundant: Silent letters can distinguish between homophones, e.g. in/inn; be/bee; lent/leant. This is an aid to readers already familiar with both words. Silent letters may give an insight into the meaning or origin of a word; e.g. vineyard suggests vines more than the phonetic *vinyard would. Silent letters may help the reader to stress the correct syllable (compare physics to physiques). The final in giraffe gives a clue to the second-syllable stress, where *giraf might suggest initial-stress. Silent letters arise in several ways: Sound changes occurring without a spelling change. The digraph was pronounced in Middle English in such words as light. Sound distinctions from foreign languages may be lost, as with the distinction between smooth rho (ρ) and roughly aspirated rho (ῥ) in Ancient Greek, represented by and in Latin, but merged to the same in English. Clusters of consonants may be simplified, producing silent letters; e.g. silent in asthma, silent in Christmas (in conservative RP, such as that spoken by Dame Vera Lynn, the is pronounced /krɪstməs/, as opposed to /krɪsməs/ in all other dialects). Similarly, with alien clusters, such as Greek initial in psychology and in mnemonic, and the much rarer clusters in chthonic and phthalate. Compound words are often simplified in pronunciation, while their spelling remains the same. For example, cupboard and breakfast were once pronounced as written, but were then simplified over time. The words forehead and waistcoat have largely reverted to their spelling pronunciations, but were once pronounced *forrid and *weskit, respectively. Occasionally, spurious letters are consciously inserted in spelling to reflect etymology (real or imagined). The in debt and doubt (from French dette, doute) was inserted to match Latin cognates like debit and dubitable. A silent was inserted in isle (Norman French ile, Old French isle, from Latin insula; cognate to isolate) and then extended to the unrelated word