Making sense of inflections and conjugated forms


Is it correct to think that the six conjugated forms listed
[here](http://ja.wikipedia.org/wiki/%E6%B4%BB%E7%94%A8) encompass a range of
ideas rather than having a inflection form directly linked to them?

For instance 未然形 is not only the negative/potential/causative that inflects to
a-sound like 食べる->食べられる 言う->言わない but also those that inflect to o-sound and
attach to the う auxiliary (or add よう, depending on whether it's a gr.1 or gr.2
verb) with probability and intention (食べよう, 言おう).

How should one generally go about distinguishing between these "forms", is it
based on general context rather than anything else (e.g. mizenkei for things
that haven't materialized yet)?




It was purely a form of inflection, but because of sound shift (食べむ → 食べよう、言はむ
→ 言おう) it collapsed.

