Introducing an explicit subject into a sentence with a topic already existing


Consider for instance the following sentence:

> わかった、忠告ありがとう。でも、ミコトがどんな子かは自分で見定める。

The obvious context is that someone has been warned about ill behavior of his
new friend by others but wants to make up his own mind.

The obvious implicit subject here is the speaker. However, the way I see it,
both:

> 私 **は** ミコトがどんな子かは自分で見定める。

> ミコトがどんな子かは私 **が** 自分で見定める。

Significantly alter the nuance of the sentence. The former would force the
second topic to become contrastive, and a non-topical subject in this context
has an entirely different nuance.

At least, I often see this pattern where a sentence seemingly “cheats” the
rule of not allowing for more than one non-contrastive topic by making the
second one implicit, almost as if Japanese actually allows multiple non-
contrastive topics just fine, but not multiple explicit ones.

The only way I see to introduce it is with particle dropping:

> 私、ミコトがどんな子かは自分で見定める。

Which “traditional grammar” teaches is not appropriate in formal contexts,
though common informally and is “technically” a grammatical mistake. But, I've
actually seen particle dropping in this context specifically multiple times in
sentences that otherwise eschewed informal grammar, suggesting that it is
indeed the only way.

So what's going on here? Is it actually not possible in sentences such as this
to introduce an explicit subject while keeping the nuance without resorting to
particle dropping, or is my understanding wrong and does
“私はミコトがどんな子かは自分で見定める。” not force the second 〜は to become contrastive? And if
so, does this only applies to less common “〜かは” situations or also to say
“その英語は好きじゃない。” vs “私はその映画は好きじゃない。” when someone is talking about a particular
film.




> The former would force the second topic to become contrastive

That’s not necessarily true. ミコトがどんな子かは is clearly shared information and the
primary topic in this context whether there’s another topic. In other words,
starting with 私は expresses what kind of person the speaker generally is and
that sounds a bit abrupt. The contrastive interpretation doesn’t really make
sense because there’s no information compared with the speaker, i.e. that
about another person.

> the rule of not allowing for more than one non-contrastive topic

There’s no such rule to begin with.

> ミコトがどんな子かは私が自分で見定める

This 私が virtually means “instead of other people”.

> The only way I see to introduce it is with particle dropping:
> 私、ミコトがどんな子かは自分で見定める。

I agree with you. Zero particle is a thing in terms of Japanese grammar, or
rather, it’s what indicates the subject in classical Japanese, and still used
today.

