Making sense of inflections and conjugated forms

Question

Is it correct to think that the six conjugated forms listed here 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)?

Answer 1

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.

Answer 2

Traditional conjugation chart was devised to explain Classical Japanese grammar, so not optimal for Modern Japanese. The greatest problem is that it no longer shows one-to-one mapping between categories and actual forms. I think this one is much better for learning purpose.

The idea 未然形{みぜんけい} comes from Classical Japanese too, named after a usage that you used to attach ば to this form to make hypothetical (yet to happen) condition, in contrast with 已然形{いぜんけい}, described realized situation (the cause of a result) with ば. So it's just a label rather than meaning.