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 and sounds still reflected by the 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 ). 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 , and English wh.