Particle TO

[rachxo]

HI! Can someone please help explain the usage of the particle to??

For example in this sentence... パーティーに間に合わないと困りますね。

What does that mean? I get the use of it in listing things or when using it to say (so and so said this) but that just confuses me. ALSO, can someone please help explain the whole causative and passive thing... the whole rareru and wareru ... etc etc is driving me crazy!!!! And the JLPT is coming up so soon

[Ongakuka]

This と is a conditional. It is similar to other conditionals like ~ば　and ~たら but usage of these often depends on context. It is quite common for と to appear after negative verbs, to mean 'if this condition isn't met, X will be/happen.' It is so with your example sentence. Here are a couple more.

勉強しないと間に合わない

パスを持っていないと入ることができない

[Adriano]

しないと　＝　しなければなりません
The "しなければなりません" was the first expression I learned to denote you must do something.
After しないといけない、and at last, the shortest expression: しないと

勉強しないと！＝I have to study!
勉強しないと、合格しません！＝If I don't study, I won't pass.