Sources:
* Akiyama, Akiyama "Japanese Grammar"
* Kaiser, Yasuko, Ichikawa, Kobayashi, Yamamoto "Japanese Grammar"
* Kim "Japanese Grammar Guide"
* Miscellaneous other sources

Completeness and accuracy not guaranteed!

# Verbs
Stem ends with one of |,w,t,r,m,n,b,k,g,s.

Bare roumaji vowels combine with c-stem:
    |V -> [nothing]
    wV -> V except wa -> わ.
    Note: tu = つ, ti = ち, si = し

"(|x)" means add x (kana and/or c-stem) if stem is |.

+: positive  >: non-past  p: plain
-: negative  <: past      P: polite

Indicative:
    +>p: -(|r)u
    ->p: -aない
        colloquial brusque form: -aん,
        written forms: -aず, -aぬ, -aざる
        conjunctive: -aないで or (written) -aず
        -aない form conjugates as verbal adjective for negative
            past, gerund, and conditional.
    +<p: replace end of stem as follows:
        | -> た
        w, t, r -> った
        m, n, b -> んだ
        k -> いた
        g -> いだ
        s -> した
            
    -<p: -aなかった
    +>P: -iます
    ->P: -iません
    +<P: -iました
    -<P: -iませんでした


Infinitive:
    -i
Gerund (nominalisation of clause):
    indic +<. s/a$/e/
    gerund of negative: -aなくて
Presumptative (intention):
    p: -(|y)oう
    P: -iましょう
Imperative:
    +p: |ろ / -e
    +p softened: -iなさい
    -p: -(|r)uな
    +P: gerund + 下(くだ)さい
    -P: -aないで ください : negative polite request/command
Conditional:
    +>: -(|r)eば
    ->: -aなければ (contraction: -aなきゃ)
    past/hypothetical: indic .<p + -ら
Potential (able/ka'e):
    -(|らr)e|
Passive:
    -(|r)aれ|
    with intransitive verb, can mean "suffering the effects of [verb]"
Causative:
    -(|s)aせ|
    shortened slang version:
        -(|s)as
        often used for causative-passive (made to do) unless ささ results
            i.e. unless | or s

## Other
Inf + た : verbal adjective: wanting to enact clause
Inf + がた : verbal adjective: difficulty of enacting clause


+<p + り : FIXME

## Exceptions
### あr
->p: ない
-<p: なかった

### Copula
+>p: だ
+>P: です
+<p: だった
+<P: でした
-..: じゃ/でわ + あr
    alternative -<P: じゃないです
gerund: で
-ve gerund: じゃなくて

Presumptative:
    p: だろう
    P: でしょう
    Append to p of another verb to form "should" presumptative.
    Also used (esp +か) to express uncertainty.

### す|
Stem for +>p indicative and conditional:
    す|
Stem for causative and passive:
    s
Stem for all other inflections:
    し|
Potential form not used (出来る(できる) used instead)

### 来| (く|)
Stem for +>p indicative and conditional:
    く|
Stem for ..P and +<p:
    き|
Stem for all other inflections:
    こ|

### 行k (いk)
+<p: いった
CHECKME: does this really apply only to 行k?

## Determining stem from +>p
No hard rule. But the following fact helps:
-a| and -o| are forbidden, as is -u| except for く| and す|.

# Verbal adjectives
Modifier:  -い
Noun:      -いの
Adverb:    -く

+>p -い
+<p -かった

+.P: +.p + です

-: -く + あr

Alternative -.P: -.p + です (slightly colloquial)

Gerund: -くて

Presumptative: [None; use copula]

Conditional:
    +>: -ければ
    ->: -くなけらば
    past/hypothetical: .<p + ら

Verbal adjectives always end with one of a,i,o,u

# Adjectival nouns
Modifier:  -な
Noun:      -なの
Adverb:    + に
Predicate: + copula

# Noun
Predicate: + copula

# Structure
Any clause can act as a noun modifier
*except* when it uses +>p copula だ

# Particles
=> https://ja.wikipedia.org/wiki/助詞
## Noun modifiers
は topic (pronounced わ)
が identifier
を direct object
に indirect object
へ towards (pronounced え)
から from
まで until
まで に by time
で various modals (in/at/on/by/within/made from/...)
の possessive/tanru
も also (inclusive topic)
も convert q to universal (but 何も is used only with negative)
か alternative (in a list)
か convert q to existential
でも convert q to "any" (universal potential)
と complete enumeration (implicit members allowed)
と result of an action (例: 作家となる) FIXME: what?
や "and/or": partial enumeration, not all necessarily apply
とか colloquial version of や
だけ only/po'o
しか except (with negative)
より comparative: greater extent than
ほど comparative: similar extent to
より from/since
的<てき> convert noun to adjectival noun

## Clause modifiers
CHECKME: always apply to indicative predicate
### Claiming the clause
けど contrast ("but", though can be neutral)
が contrast (politer)
けれど contrast (formal)
のに despite
から because
ので because (politer)
し because; one of a partial enumeration of causes
ながら during

### Not claiming the clause
なら/ならば if; FIXME: difference from directly using conditional?
    can also modify a noun; FIXME: meaning?
と if; indicates that the implication is obvious/natural
と du'u (indirect speech, expressing thoughts, etc)
と direct quotation
こと nominalise (nu)
の/ん nominalise (ka)
か indirect question
べき should/must happen
って casual quote and/or subject marker; often elliptical

## Sentence modifiers
か polite question marker (default xu)
ね right?
よ !
わ (dated?) "feminine" softener; emphasis

# Common contractions
ては -> ちゃ/て, では -> じゃ/で (gerund as topic)
-ている -> -てる
https://en.wikipedia.org/wiki/Japanese_grammar#Colloquial_contractions