Why are the verb classes called ichidan and godan?


Is there a particular reason why verbs are classified as "class 1" verbs
(一段動詞) and "class 5" verbs (五段動詞)? Where did class 2 to 4 go? Do or did they
exist at all, and why (not)?

Thanks!




Before considering modern Japanese, I think that it is easier to understand
this by first understanding classical. Classical Japanese has three major
regular verb classes: quadrigrade (四段), monograde (一段), and bigrade (二段). Both
monograde and bigrade may further be sub-divided into upper (上) and lower (下).
There are also four irregular classes: k-irregular, s-irregular, n-irregular,
and r-irregular. Verbs are conjugated into six forms: irrealis (未然形),
adverbial (連用形), conclusive (終止形), attributive (連体形), realis (已然形), and
imperative (命令形).

Let's consider the quadrigrade verb kak- 'to write' (書く). When conjugated to
each of the above forms, it becomes kak-a, kak-i, kak-u, kak-u, kak-e, kak-e.
Notice that the distinctive suffixes are a, i, u, e. The total number of
distinctive suffixes is four, which is why this is called quadrigrade (四段).

Next, let's consider the monograde verb mi- 'to see' (見る). When conjugated to
each of the above forms, it becomes m-i, m-i, m-iru, m-iru, m-ire, m-iro.
Notice how all of the forms contain a single -i. This is why it is called
monograde (一段). Now let's consider the verb tabe- 'to eat' (食べる). It
conjugates as tab-e, tab-e, tab-eru, tab-eru, tab-ere, tab-ero. This time all
of the forms contain a single -e. This too is monograde. To distinguish
between these two, those ending in -i are called upper monograde and those
ending in -e are called lower monograde. The normal vowel ordering in Japanese
is a, i, u, e, o. Notice that comparing i and e, i comes first and e comes
second. Traditionally these would be written vertically. As a result, i is
considered to be "upper" and e is "lower" in this chart, hence the names.

Next let's consider the bigrade verb ok- 'to rise' (起く). (Older form of modern
oki- 起きる 'id'.) When conjugated to each of the above forms, it becomes ok-i,
ok-i, ok-u, ok-uru, ok-ure, ok-i[yo]. All forms have an -i or -u in it. This
is a two-way distinction, hence the name bigrade. Now let's consider the
(older) verb tab- 'to eat' (食ぶ). This conjugates as tab-e, tab-e, tab-u, tab-
uru, tab-ure, tab-e[yo]. Again there is a two-way distinction, so this too is
bigrade. However, this time the distinction is between -u and -e. As such,
bigrade may be sub-classified into upper bigrade (i/u) and lower bigrade
(u/e).

The four irregular verb classes are simply irregular which explains their
names.

Now let's look at modern Japanese. Modern Japanese simplifies much of the
above: all quadrigrade verbs have now become quintigrade (五段), bigrade verbs
have gone bye-bye (pun intended), and two of the four irregular classes have
disappeared. Also note that the conjugation class formerly known as realis
(已然形) is now known as conditional (仮定形).

Let's consider the new quintigrade verb. In addition to the four distinctions
earlier, there is now a fifth, hence the name. This fifth form is -o. This can
be seen in kak-o: "(I) shall write, let's write". However, this form is
secondary in nature: it derives from kak-au (and earlier kak-amu). -au-
regularly changes into o: (long o). This -a is the same -a as seen in the
irrelias (未然形). This is not a true form, but is added to by-pass the
phonological explanation.




Before considering modern Japanese, I think that it is easier to understand
this by first understanding classical. Classical Japanese has three major
regular verb classes: quadrigrade (四段), monograde (一段), and bigrade (二段). Both
monograde and bigrade may further be sub-divided into upper (上) and lower (下).
There are also four irregular classes: k-irregular, s-irregular, n-irregular,
and r-irregular. Verbs are conjugated into six forms: irrealis (未然形),
adverbial (連用形), conclusive (終止形), attributive (連体形), realis (已然形), and
imperative (命令形).

Let's consider the quadrigrade verb kak- 'to write' (書く). When conjugated to
each of the above forms, it becomes kak-a, kak-i, kak-u, kak-u, kak-e, kak-e.
Notice that the distinctive suffixes are a, i, u, e. The total number of
distinctive suffixes is four, which is why this is called quadrigrade (四段).

Next, let's consider the monograde verb mi- 'to see' (見る). When conjugated to
each of the above forms, it becomes m-i, m-i, m-iru, m-iru, m-ire, m-iro.
Notice how all of the forms contain a single -i. This is why it is called
monograde (一段). Now let's consider the verb tabe- 'to eat' (食べる). It
conjugates as tab-e, tab-e, tab-eru, tab-eru, tab-ere, tab-ero. This time all
of the forms contain a single -e. This too is monograde. To distinguish
between these two, those ending in -i are called upper monograde and those
ending in -e are called lower monograde. The normal vowel ordering in Japanese
is a, i, u, e, o. Notice that comparing i and e, i comes first and e comes
second. Traditionally these would be written vertically. As a result, i is
considered to be "upper" and e is "lower" in this chart, hence the names.

Next let's consider the bigrade verb ok- 'to rise' (起く). (Older form of modern
oki- 起きる 'id'.) When conjugated to each of the above forms, it becomes ok-i,
ok-i, ok-u, ok-uru, ok-ure, ok-i[yo]. All forms have an -i or -u in it. This
is a two-way distinction, hence the name bigrade. Now let's consider the
(older) verb tab- 'to eat' (食ぶ). This conjugates as tab-e, tab-e, tab-u, tab-
uru, tab-ure, tab-e[yo]. Again there is a two-way distinction, so this too is
bigrade. However, this time the distinction is between -u and -e. As such,
bigrade may be sub-classified into upper bigrade (i/u) and lower bigrade
(u/e).

The four irregular verb classes are simply irregular which explains their
names.

Now let's look at modern Japanese. Modern Japanese simplifies much of the
above: all quadrigrade verbs have now become quintigrade (五段), bigrade verbs
have gone bye-bye (pun intended), and two of the four irregular classes have
disappeared. Also note that the conjugation class formerly known as realis
(已然形) is now known as conditional (仮定形).

Let's consider the new quintigrade verb. In addition to the four distinctions
earlier, there is now a fifth, hence the name. This fifth form is -o. This can
be seen in kak-o: "(I) shall write, let's write". However, this form is
secondary in nature: it derives from kak-au (and earlier kak-amu). -au-
regularly changes into o: (long o). This -a is the same -a as seen in the
irrelias (未然形). This is not a true form, but is added to by-pass the
phonological explanation.

