「どうせ誰もいはしないと高をくくっていたところもある。」
This one's throwing me for a bit of a loop. The translation says "He also didn't really take the possibility of anyone being there seriously."
It makes sense to me except for the いはしない part. What does this mean?
I looked up い and saw that it can mean stomach, so my first thought was that いはしない was perhaps some idiom like "not doing his stomach" that means "not being there" but I can't find any evidence to justify that on the internet so I have to assume it's wrong.
The sentence is not about someone's stomach. If it were, 「い」 would have certainly been written in kanji as 「胃{い}」. Besides, 「胃はしない」 makes no sense to begin with.
「Verb in 連用形{れんようけい} (continuative form) + は + しない」
= "would not (verb) one bit" ← rather emphatic
「い」 is the 連用形 of the verb 「いる」 ("to be", "to exist").
「誰{だれ}もいはしない」, therefore, means "no one would be (there)"
You will encounter this grammar pattern over and over. That I can guarantee.
Note that the 「は」 is occasionally replaced by a 「や」 in more informal speech.
I have noticed over the years that when the single-syllable 連用形 of some of the two-syllable verbs (two in dictionary forms) is used in phrases and sentences, quite a few Japanese-learners do not seem to even notice that they are seeing/hearing a verb there. Verbs are too important to just not notice in any language. Those verbs include:
「い」 for 「いる」
「し」 for 「する」
「き」 for 「来{く}る」 and 「着{き}る」
「み」 for 「見る」, etc.
「し」 is the one most often used and this website is indeed full of questions regarding phrases containing it.
