Difference between "ga" vs "wo"

Question

It's known that roughly, in most cases, we can think of using "wo" vs "ga" this way:

ga is used when action is abstract, mental, non-physical

otherwise, wo is used

Yet, these examples are in contradiction with that rule:

Something ga taberarenai.

Someone wo shitte iru.

Why is that? Are there any exceptions?

There are other examples as well I can remember for now.

Answer 1

As for your first example, potential forms of transitive verbs can take が instead of を. 食べられない (taberarenai) is the negative potential form of 食べる (taberu, "to eat"). が is used because no physical action has been taken yet when you say "can".

• Potential Form

  The potential form indicates that something is possible but no actual action is actually taken. While the potential form is still a verb, because it is describing the state of feasibility, in general, you don't want to use the direct object 「を」 as you would with the non-potential form of the verb.

• The difference between が and を with the potential form of a verb.
• Why say "〜、皆には出来る。" instead of " 〜、皆は出来る。" in this context?

  One key to understanding how できる happens grammatically is that できる is often describing the thing that can be done, instead of the people or things doing the thing. Sometimes a closer gloss is doable rather than can

As for your second example, yes, 知る (shiru, "to learn; to get to know") is a transitive verb (a verb that takes を). 分かる (wakaru, "to understand") is a similar word but does not usually take を. I think this is something you have to remember and get used to.

• How should I choose between [知]{し}る and わかる?
• 知る vs わかる and when to use が and を in "how to" questions