You can use the report a problem button during lessons to report mistakes and alternative translations. The course is still in beta, so the course builders need help from users like you to include missing alternative translations!
I always do use the report a problem button, but I also make a comment at the same time because the report a problem button gives no opportunity to make the case of why one thinks one is right.
Still not accepted as of 2015-01-05, just like many other correct variants elsewhere involving need not and especially needn't. This almost looks like systematic omission by someone who thinks it's wrong.
What is the infinitive of "hoef"? I am confused by which verb this is, it looks like "hebben" but it isn't... or is it?
The infinitive is hoeven, and its meaning is: to be necessary. Maybe remember it like this: If it behooves you to do something, it means that it's necessary for you to do it.
A fundamental thing you need to understand is that the Dutch infinitive translates both the English infinitive and the English gerund. In English, some verbs require an extended infinitive such as "[I want] to swim" and some require a gerund such as "[I consider] swimming". For some ("I love ...") both are possible, with or without a change in meaning, and some even take a bare infinitive such as "[I can] swim". The situation in Dutch is similar but simpler.
Hoeven is the modern form of (antiquated) behoeven, an obvious cognate of to behoove. The following overly literal translation to Shakespearean English leverages your English intuitions for understanding why (or at least remembering that) the word te is needed here:
- Ik (be)hoef niet te zwemmen.
- It behooves me not to swim.
The translation would be even more obvious if Dutch had "Het behoeft me niet te zwemmen" or English had "I behoove not to swim", but at least in this case the two languages still agree on whether te / to is required. (Occasionally they disagree about that.)