のに

彼は泳げないから、船もないのに、そんな島まで行けっこない。
Hi. I read this sentence in a textbook and I have some problems with the のに. Usually のに is for 逆接 but the のに in this case seems to mean just "because". Why can のに be used this way? Could you please explain the のに?
Thank you.

っこない negates the whole part preceding it in that sentence, not only そんな島まで行ける. Thus, 船もないのに、そんな島まで行ける is negated.
cf.
雨が降っているのに、濡れないはずがない。 ＝ 「雨が降っているのに、濡れない」はずがない。
努力もしていないのに、できるようになるわけがない。 ＝ 「努力もしていないのに、できるようになる」わけがない。

This is confusing enough, but から also works well in these sentences. In this case, it's considered that only the main clause is negated.

船もないから、そんな島まで行けっこない。
雨が降っているから、濡れないはずがない。
努力もしていないから、できるようになるわけがない。

Incidentally, when から is used instead of のに in your example, it should be 彼は泳げないし、船もないから、そんな島まで行けっこない。 to avoid repeating から.

Thank you. I see.

Sorry for resurrecting this thread, but I thought it would be interesting to get @Toritoribe さん's thoughts on the matter, which is closely related (but different in an interesting way) to the examples above.

Anyhow, a user on Reddit cited brought up this sentence:

確かな根拠もないのに論文は書けない。

Click to expand...

It's another example of this sort of usage of のに in Japanese where it could be replaced with から (and therefore seems, at a glance, as if のに has the opposite meaning of the usual "even though"/"despite", etc.)

It's different in the sense that you don't have a separate structure at the end like ～っこない or ～わけがない to negate the sentence but rather, simply a negative verb in itself. I believe one of my Japanese teachers, way, way back in the dark ages explained this very similarly to Toritoribe-san's explanation above, i.e. to think of it as 確かな根拠もないのに論文は書け（る） as being negated.

I'm just curious if that's also how Toritoribe-san would analyze this example.
(Anyhow, sorry for the semi-necropost, but I thought it might be appropriate in this case, and hopefully someone will find this example interesting/enlightening.)

Yes, I think the basic structure is the same. The key is, of course, whether the main clause is negative or not. If it's affirmative, this phenomenon "のに and から/ので are seemingly interchangeable" doesn't occur.

○確かな根拠があるから/ので、論文が書ける。
×確かな根拠があるのに、論文が書ける。

○確かな根拠もないのに、論文を書く。
×確かな根拠もないから/ので、論文を書く。

○船があるから、そんな島まで行ける。
×船があるのに、そんな島まで行ける。

○船もないのに、そんな島まで行った。
△船もないから/ので、そんな島まで行った。

The last example sentence can make sense in an appropriate context, for example, the subject went to the island to get a ship, i.e., ここには船もないから/ので、そんな島まで船を手に入れるために行った。. Needless to say, the meaning is completely different from 船もないのに、そんな島まで行った。 in this case, and ここには船もないのに、そんな島まで船を手に入れるために行った。 is ungrammatical. Thus, のに and から/ので are not interchangeable, anyway.

Thank you, Toritoribeさん! I'm glad that your analysis of this coincides with how I remember my professor explaining it back in the dark ages.

(For what it's worth, I shared an example combining what you mentioned here and what my professor explained long ago, and the user on Reddit said it was the first time this construction "clicked" for them, so thank you on their behalf as well.)

And yes, your additional example sentences all make sense and help to clarify the matter further. のに is one of those interesting cases where many of the usages it appears in aren't so difficult for an English-native Japanese-as-a-second-language learner to process, but certain cases can cause confusion. This explanation and analysis, I think, is very helpful for a learner to get a full grasp of the way のに functions in Japanese.