NB: This page is under construction. Comments on more verb conjugations will be added later.
These two forms are often grouped together, as depending on context either can mean if or when in English. (McClure [below] devotes 10 pages to discussing the nuances.) To quote some examples from McClure:
The President may or may not be scheduled to go by. I won't wave my flag until he is going by. This sentence emphasises the order of events.
If the President goes by, I will wave my flag.
The President may or may not go by. If he actually does appear, I will wave my flag. The sentence makes clear the conditions under which flag-waving will in fact occur.
If the President is going to go by, I will wave my flag.
Given that the President is in fact going to drive by, I will wave my flag, perhaps starting immediately. The sequence of events is not relevant.
The -ますなら(ば) form has the rare alternative of -ませば.
The potentiality of a verb can be expressed in a couple of ways. One is to use 出来る (to be able to) as an auxiliary verb:
If there is a close relationship between a direct object and the verb, the "をVこと" can be omitted, i.e.
The other is the potential form of the verb, typically constructed by adding られる to the base (一段 verbs) or adding る to a potential base formed by changing the last kana of the plain form from the う column to the え column (読む to 読める, 話す to 話せる, etc.) (五段 verbs). The potential form is itself an 一段 verb, and is an intransitive verb, generally taking the particle が instead of を.
The special class of single-kanji する verbs (害する, 愛する, etc.), which are marked as "vs-s" in WWWJDIC, have a potential form which ends in either しえる or しうる. The two are inter-changeable, (however just to complicate matters, the しうる form is not 五段, and does not inflect further; other inflections must be derived from the しえる form.) Some of these verbs also have a せる potential, which denotes capability to carry out something, and appears to be rather colloquial.
The causative form of a verb indicates that someone is made or allowed to perform the action. It is formed by adding させる to the base (一段 verbs) or せる to the negative base (五段 verbs)
There is an alternative form in which the せる is replaced by す. Thus there is 話さす instead of 話させる, etc. This form often has a nuance of more direct causation, for example 食べさす has a sense of feeding someone, rather than just making them eat.
I have used the label volitional/hortative to describe a set of verb forms which are often combined with the conjectural category (below) and called "presumptive". What I mean by volitional/hortative are the forms of verb that:
Formation usually involves the -おう/こう/.../よう and -ましょう inflections in affirmative statements. For example:
As the -おう/こう/.../よう and -ましょう forms have no negative, the まい ending is sometimes used in the situation of expressing negative intention. It cannot be used to express a "let's not" situation, and in any case is a literary form and rarely seen at the ends of sentences, however it is fairly common in a dependent clause to show one's strong determination not to do something, as in
Another construction which means "let's decide to" or "let's try to" is verb+ことにしよう/しましょう or verb+ようにしよう/しましょう. For example:
Note that that are many verbs where the volitional/hortative forms cannot be used in a meaningful way. One cannot say "午後に雨が降りましょう", for example. On the other hand, one might hear rockers on the stage yelling:
This category of verb inflection is also often included in the broad presumptive category, and indeed there is some crossover between them. I have chosen to call it "conjectural", but it is also called "tentative" in some texts.
Strictly speaking, it is not a conjugation at all, as it usually involves the addition of the auxiliary だろう (formal: でしょう) to the informal form of the verb, both non-past and past. It expresses the speaker's belief that something may be the case, including past and future occurrence or non-occurrence of events of which he is not the author. Its closest English equivalent would be "probably", and when used in questions, it has a softening effect.
The -ないだろう form has the literary alternative form: なかろう.
The しろ imperative form of する has an literary alternative せよ.
William McClure: Using Japanese: a Guide to Contemporary Usage, Cambridge University Press.
My thanks to Bart Mathias and Shoji Yamazaki for their significant assistance with the verb conjugation option in WWWJDIC and with the preparation of these notes.