You are likely quite familiar, but I highly recommend Jay Rubin’s excellent book to anyone here, “Making Sense of Japanese”, the “Wa and Ga” chapter in particular. Relevant excerpts:
Ga always marks the subject of a verb or adjective, and if that verb is the main verb, that means ga is marking the subject of the sentence. Wa never does this.
Wait a minute. Did I just say that _wa never marks the subject of a sentence? Yes, and I mean it. … _Wa only marks a topic of discussion, “that about which the speaker is talking.” And, as Anthony Alfonso so sensibly remarks, “Since one might talk about any number of things, the topic might be the subject of the final verb or time, or location, etc.”
He then goes on to make the exact point you made earlier (that I agreed with here):
Alfonso’s remark about the possible contents of a topic suggests that a wa topic can be the subject of a sentence, but I am still going to insist that it never is.
He then gives the example of 私は行きました, using his “old standby” as a translation:
“As for me, [I] went.” The “I” is in brackets here because it is present in the Japanese sentence only as an unspoken subject. Watashi is not the subject of the sentence. It is simply the topic of the upcoming discussion. … The subject of the verb ikimashita is not watashi but the silent pronoun that follows it.
He uses the words “unspoken subject”, “zero pronoun”, and “silent pronoun” at various points for what I’ve been calling “implied” subjects (in brackets) in the diagrams.
All of this is to explain how I interpret the three-は example from the manga as well as the examples from the Tofugu article:
難しくない。
[あれ] [が] 難しくない
it’s not-difficult
Subject: あれ (implied), Predicate: 難しくない (an adjective meaning not-difficult)
If you add the は, though, it changes subtly but significantly:
難しくはない
They translate this as “It’s not (exactly) difficult”, but I’d express it this way:
難しくはない
難しくは [あれ] [が] ない
As to difficulty, it is not
Topic: 難し[さ], Subject: あれ (implied), Predicate: ない (a simple verb meaning non-existent)
I’m fairly certain I’ve got it right and this is how it works, but still welcome any further feedback or corrections. (Certainty is a red flag for me!
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