Which part of speech is the 「ぞ」 {zo} in 「神のみぞ知るセカイ」 {kami nomi zo shiru sekai}?

Question

「神のみぞ知るセカイ」 {kami nomi zo shiru sekai} is the title of a manga/anime series but I'm not asking about the anime. I'm just curious with the 「ぞ」 {zo} part in the title.

I know there is a {zo} particle that is similar to {yo}, such that {iku zo} is similar to {iku yo}. But I have never encountered {yo} nor {zo} in the middle of a sentence/clause before, so this made me curious.

Which part of speech is that {zo}? What connotation does it bring and how do we use it in a sentence?

p/s: I know the {zo} is not a part of {nomizo} because when I entered {nomizo} in my Japanese dictionary software it only returned {nomi} = “only" so I deduced that the {zo} is a separate word.

Answer 1

If you look at koujien's entry for ぞ there are several uses (mostly outdated), but I think the one which applies here is: 一つの事柄を特に指定し強調する｡ In other words, it places emphasis on something specific. So in reguards to this light novel/anime series title I think it places emphasis on the fact that the/a world which ONLY GOD knows about.

Also, this reminded me of a famous quote of Sakamoto Ryouma 世の人はわれは何ともいはばいへ わがなすことは我のみぞ知る something like "No matter what society says, I know the meaning to my own actions" basically, screw what society says, because I know the path I want to go down.

I believe he's emphasizing that what matters is that HE knows what he should be doing.

Answer 2

It's an emphatic particle from old Japanese. Only God/Gods. There's another one used with questions to show more uncertainty. "どこぞで休んでいくか"　(デジタル大辞泉)

Answer 3

「ぞ」　is the particle, which normally used at end of the phrase (終助詞), to express some forcefulness to the expression.

There is also another form 「ぜ」, which is unpolite way to express forcefulness.

Those also explain at wikipedia

• http://en.wikipedia.org/wiki/Japanese_particles