foreign pronunciations of these words inevitably only approximated the original chinese, and many distinctions were lost. in particular, korean and japanese had far fewer consonants and much simpler syllables than chinese, and they lacked tones. even vietnamese merged some chinese initial consonants (for example, several different consonants were merged into "t" and "th" while "ph" corresponds to both "p" and "f" in mandarin). a further complication is that the various borrowings are based on different local pronunciations at different periods. nevertheless, it is common to treat the pronunciations as developments from the categories of the middle chinese rhyme dictionaries.