The difference between them? Irregular. I recommend you memorise a lot of examples, because it's faster than wonder why they're so.isshuu-one week
It depends on the fact that some numbers end with an unstressed syllable formed by a stop consonant and an "i" or "u". In these cases, when the following counter begins with a voiceless stop or an "s" (note that in Old and Middle Japanese "h" was pronounced "p" [ɸ], so it counts as a stop, and sometimes it has become, intervocalically, w, like in the particle は), the vowel was dropped and the two sounds merged. It happens also with jū (it was pronounced zipu in Middle Japanese). The process is very regular.there are excpetions to how counters are pronounced depending on what number they are used with
The pronunciation was extremely unpopular already in the last century. The assimilated form of jū now is juppai by analogy of more regular numbers such as roku v. rop (as in roppai).十 => zipu + pai > zippai > jippai
This depends on the vocabulary. While wa written 話 never changes pronunciation, wa witten 把 and 羽 follow the assimilation rule. But the assimilation is not mandatory, at least in some cases; e.g., rokuwa no usagi, or six rabbits, is not unheard of.A common counter is wa 話 (for example roppa).
Hi, Flaminius.While wa written 話 never changes pronunciation, wa witten 把 and 羽 follow the assimilation rule.