Topic は vs. direct object を for "I have never X"


The sentence pattern for "I have never X" is covered in this question: [Is
there a form for "I have never heard
of"?](https://japanese.stackexchange.com/questions/3930/is-there-a-form-for-i-
have-never-heard-of/3932)

However, I'm confused on which particle to use for the noun in this sentence
pattern. For example:

From a Japanese children's book:

> こんなに大きなももはみたことがない。  
>  "I have never seen a peach as large as this."

Notice that it uses は after もも. Here is a second example from the cited
question.

> その歌{うた}を聞いたことがありません。  
>  "I have never heard that song before."

It uses を after うた.

Are both particles acceptable? Do they convey different meanings?




I disagree with Kaji's analysis. While Kaji's is the textbook answer
concerning the question when _-wa_ is used, the explanation remains opaque.  
Rather there is a _-wa_ after _momo_ in the first example, because we can
assume that the speaker has, at some time, seen big peaches. The one referred
to in the sentence, however, is, among those seen, the biggest.  
That is not the case with the second example, though. I understand the
sentence to imply that the speaker hasn't heard that specific song before, but
not that s/he has NEVER heard **a song** before.  
So, the answer to your question is: yes, both particles are good, but they
imply different things about the noun to which they are attached.




I disagree with Kaji's analysis. While Kaji's is the textbook answer
concerning the question when _-wa_ is used, the explanation remains opaque.  
Rather there is a _-wa_ after _momo_ in the first example, because we can
assume that the speaker has, at some time, seen big peaches. The one referred
to in the sentence, however, is, among those seen, the biggest.  
That is not the case with the second example, though. I understand the
sentence to imply that the speaker hasn't heard that specific song before, but
not that s/he has NEVER heard **a song** before.  
So, the answer to your question is: yes, both particles are good, but they
imply different things about the noun to which they are attached.

