Before the influx of Sino-Japanese vocabulary into the Japanese lexicon, only numbers of native origin existed. Counters still existed at this time, as this is a grammatical feature common across many language families in Eastern Asia. Counters were naturally limited to native numbers, creating a very intuitive and easy-to-use system.
Nonetheless, Sino-Japanese numbers have been used for most of Japan's written history, including most of the period associated with Classical Japanese. As such, it would be unwise to simply ignore how Sino-Japanese numbers would have been used up until modernity. For instance, 四百 at one point would have been read as しひゃく, despite that not being so today. This is evident in Modern Japanese in rare but extant four-character idioms such as 四百余州 (all of China; literally "approximately 400 provinces") and 四百四病 (every kind of disease; literally "four hundred four" diseases).
Having said this, there are still two paradigms to thoroughly investigate in Classical Japanese: native numbers and Sino-Japanese numbers. Inevitably, the mixing of the two would have occurred in the spoken language well before this became evident in the written language. To this day, a lot of variation exists due to the mixing of the two. However, our first task will be to see how native numbers would have been used as a fully functioning numeric system when used in isolation.
It may come as a surprise to you that the native numeric system of Japanese, or at least Old Japanese, could theoretically count from 0 to 99,999. Although it is unlikely any speaker would have actually counted that far, the patterns were in place to make such counting possible.
Very few cultures developed an actual number for 0, and one could say that Japanese was not one of those cultures, but the word なし, literally meaning "nothing", can be viewed as a close approximation to the concept of 0 when used in a numerical connotation.
In the chart below, the most relevant numbers from 0 to 90,000 are listed along with their corresponding counter phrases. Note how the counter つ is used consistently from 1-9, that no counter is used for 10, and that 20/30 are used with the counter ち・ぢ. Outside these numbers, no actual counters are attached to numbers when using them as counter phrases.
|99,999||ここのよろず ここのち ここのほ ここのそ あまり ここの||← 同|
1. When counter-less, numbers were originally disyllabic.
2. The sounds in parentheses would drop out and or stay in some words. For instance, むゆか (six days; sixth day of the month), survives in Modern Japanese as むいか.
3. It is posited by some that 5 was originally just い and that つ was added to make it disyllabic, but the sense of the word being two morphemes was lost, which gave way for いつつ to be formed.
As far as counters are concerned, the exceptions found in Modern Japanese with Sino-Japanese endings are the same for the most part. For example, the counter for people is -人（にん） for Sino-Japanese numbers and ～人（たり） for native numbers. ～人 is ～人（り） for ひと (1). In Modern Japanese, the native counter is normally only used for 1-2, but in Classical Japanese there was no such restriction. Native counters can be used with any native number, except 0 of course and likewise Sino-Japanese counters with Sino-Japanese numbers.
There are some counters that are noticeably different. For example, the counter for year is とせ instead of とし. The counter for days was ～か too, but it was used with any number. For example, 100 days was ももか. The exceptions with ～か were minus small changes. っ found in some can't be attested throughout history because っ wasn't written until much later. But, they were probably pronounced with them. 6 days (of the month) and 7 days (of the month) in particular were むゆか and なぬか instead of むいか and なのか respectively.
Again, around the sixth month and fourth year of the Jishou Era, there was a sudden capital move.
From the 方丈記.
To begin with, as for hearing about the rise of Heiankyou, it has already been four hundred years since the capital was determined in the reign of Emperor Saga.
From the 方丈記.
When the moon of the eleventh day was about to disappear
From the 伊勢物語.
Eight/a lot of clouds
On the same seventh day of the month
From the 平家物語.
6. 一坏乃 濁酒乎 可飲有良師
It seems better to drink a cup of cloudy sake.
From the 万葉集.
If two people hit (the dog), would it still live?
From the 枕草子.
The sixth. The same as yesterday.
From the 土佐日記.
People who pinned their hopes on people of rank and relied on their favor, even for a day quickly try to use their energies to move, and people who were left behind by society and had nothing to hope for stay put and complain.
From the 方丈記.
Reading Note: 一日 could also be read as ひとひ in the ancient period. Although つひたち and いちにち existed as well, this reading could also be used to mean "the other day" or "all day". The latter reading is actually acceptable today in more so written Japanese, but it is normally replaced with 終日 or 一日中.