Is it just me or is this answer's wording kind of ambiguous and confusing? Despite the 9 votes it's amassed so far, I am having a hard time understanding its content accurately. I was trying to go through the post and fix grammar issues and improve readability and clarity, but I was not sure I understood the author's intent. I'd post a comment requesting further clarification from the answerer, but since this is an old answer, and seeing how the answerer may not be active any more and the follow-up comment from the OP hasn't been responded to, I figured it might be better to write a meta post. By posting this, I intend to pose this question: Is it possible to solicit community effort on older posts?
The answerer claims:
It's basically the moment when someone did a verb (past tense), receive a change in state, and the result can be seen clearly as a consequence of the verb.
食べている I am eating
notice that here the action 'eat' has been done. The speaker is in the state of eating as a consequence of doing the verb eat and start on the moment after the speaker bite, chew, and swallow. We regard this as progressive verb because as you did the verb, it is continuous.
But if they meant to say ている expresses "a consequence of the verb", shouldn't it be "I have eaten" instead of "I am eating"? I am not sure what "in the state of eating as a consequence of doing the verb eat" is intended to mean. I can't wrap my head around "as you did the verb, it is continuous" either. Is the answerer talking about "eat" as happening in an instant or as a continuous action?
落ちている It's on the ground
Here, you don't say that this means it is falling. Now imagine a coin is falling in the air from a table in midair. This coin hasn't done the verb 'fall', after all if this coin has done it, then we'd say the past tense (fell) while it is in the midair (which is weird).
I think I roughly understand what the answerer is trying to say in this paragraph above, but I think it needs some work.
verb + ing doesn't always mean progressive verb because some are instantaneous and doesn't possess the continuous manner (like the verb 'fall'). This type of verbs then, when changed into + ing, will mean that it is on the progress that the verb is going to be done (but not yet done... it's like on it's way to do the verb). (not the progress after the verb had begun).
It is unclear what the answerer is arguing here. Are they using English verbs as a way to categorize Japanese verbs? But I think it's fair to say English and Japanese have different ways of differentiating between action verbs and stative verbs. Some verbs considered action verbs in English may fall squarely under stative verbs in Japanese, and vice versa. The answerer didn't make it clear what they are talking about here. Nor is it clear whether they are setting apart from the the two verbs already discussed a new category of verbs with this passage.